Research Article Investigation of Through-Thickness...
Transcript of Research Article Investigation of Through-Thickness...
Hindawi Publishing CorporationInternational Journal of Engineering MathematicsVolume 2013 Article ID 676743 11 pageshttpdxdoiorg1011552013676743
Research ArticleInvestigation of Through-Thickness Stresses inComposite Laminates Using Layerwise Theory
Hamidreza Yazdani Sarvestani and Ali Naghashpour
Concordia Centre for Composites (CONCOM) Department of Mechanical and Industrial EngineeringConcordia University 1455 De Maisonneuve Boulevard West Montreal QC Canada H3G1M8
Correspondence should be addressed to Hamidreza Yazdani Sarvestani h yazdencsconcordiaca
Received 13 August 2013 Revised 10 October 2013 Accepted 11 October 2013
Academic Editor George S Dulikravich
Copyright copy 2013 H Yazdani Sarvestani and A Naghashpour This is an open access article distributed under the CreativeCommons Attribution License which permits unrestricted use distribution and reproduction in any medium provided theoriginal work is properly cited
In this study an analyticalmethod is developed to exactly obtain the interlaminar stresses near the free edges of laminated compositeplates under the bending moment based on the reduced form of elasticity displacement field for a long laminate The analyticaland numerical studies were performed based on the Reddyrsquos layerwise theory for the boundary layer stresses within cross-plysymmetric angle-ply and general composite laminates Finally a variety of numerical results are presented for the interlaminarnormal and shear stresses along the interfaces and through thickness of laminates near the free edges The results showed highstress gradient of interlaminar normal and shear stresses near the edges of laminates
1 Introduction
Due to high specific strength and stiffness of fiber reinforcedpolymer composite laminated composites have found aug-mented use inmany industrial applications In the boundary-layer regions due to geometry and material discontinuitiesthe interlaminar stresses exhibit much higher values thanthose predicted by the classical lamination theory (CLT)These highly concentrated stresses cause delaminate fail-ure in the laminates However no exact solution is foundfor elasticity equations because of inherent complexitiesinvolved in the problem of finding exact stress values in theedges Hence different analytical and numerical methodsfor finding the interlaminar stresses are used to describethe interlaminar stresses at the free edges of compositelaminates Complete literature surveys on this subject areavailable in review articles of Kant and Swaminathan [1]which obviously show the detailed path of developmentof methods The first approximate analysis of interlaminarstresses was presented by Puppo and Evensen [2] Theystudied interlaminar shear stresses in an idealized lami-nate consisting of orthotropic layers separated by isotropicshear layers with interlaminar normal stress being neglectedthrough the laminate Other approximate analytical methods
utilized to examine the problem consist of the use of thehigher-order plate theory by Pagano [3] the perturbationtechnique by Hsu and Herakovich [4] the boundary layertheory by Tang and Levy [5] and the approximate elasticitysolutions by Pipes and Pagano [6] An approximate theoryis also employed by Pagano [7] based on the assumedinplane stresses and the use of Reissnerrsquos variational principleWang and Choi [8] utilized Lekhnistskiirsquos stress potentialand the theory of anisotropic elasticity for examining thefree edge singularities A variational approach concerningLekhnitskiirsquos stress functions is used by Yin [9] for theevaluation of free-edge stresses in laminates under uniaxialtension bending and torsion Wang and Crossman [10]developed a quasi-three-dimensional finite element solutionto determine the free-edge stresses in a symmetric balancedcomposite laminate under uniaxial tension and uniformthermal loading Whitcomb et al [11] studied the differencesin numerical results for interlaminar stresses obtained byvarious methods (finite difference methods finite elementmethods and perturbation techniques) Boundary elementmethod and the integral equation theory were used byDavı [12] to study the stresses in a general laminate underuniform axial strain Carrera and Demasi [13 14] studiedthe accuracy of the finite-element mixed layerwise solutions
2 International Journal of Engineering Mathematics
y
z
x
a
a
2b
MO
MOh
Figure 1 Laminate geometry and coordinate system
by using the Reissner mixed variational theorem (RMVT)They compared the numerical results for interlaminar stressesin several finite-element models and elasticity theory withincomposite laminates and sandwich plates Nguyen andCaron[15] employed a multiparticle finite element method to studythe interlaminar stresses near the free edges of generalcomposite laminates under mechanical and thermal loadingRobbins and Reddy [16] used a displacement-based variablekinematic global-local finite elementmethodMittelstedt andBecker [17] utilizedReddyrsquos layerwise laminate plate theory tofind the closed-form analysis of free-edge effects in layeredplates of arbitrary nonorthotropic layups The approachconsists of the subdivision of the physical laminate layers intoan arbitrary number of mathematical layers through the platethickness Na [18] used a finite element model based on thelayerwise theory He employed the von Karman type nonlin-ear strains to analyze damage in laminated composite beamsIn his formulation the Heaviside step function is employedto express the discontinuous interlaminar displacement fieldat the delaminated interfaces Plagianakos and Saravanos [19]presented a higher-order layerwise theoretical frameworkwhich enables prediction of the static response of thick com-posite and sandwich composite plates Ullah et al [20] carriedout some experimental tests to characterize the behavior of awoven CFRP material under large-deflection bending Two-dimensional finite element (FE) models were implementedin the commercial code Abaqus They performed series ofsimulations to study the deformation behavior and damage inCFRP for cases of high-deflection bendingHelenon et al [21]presented an experimental and numerical investigation intofailure of T-shaped laminated composite structures Threeout-of-plane bending cases are studied They found thatvery high free-edge maximum principal transverse tensilestresses perpendicular to the fiber direction occur at thefailure locations Thai et al [22] indicated an isogeometricfinite element formulation for static free vibration and buck-ling analysis of laminated composite and sandwich platesTheir method allows removing shear correction factors andimproves the accuracy of transverse shear stresses Thai et al[23] investigated the behavior of laminated composites usingseveral high order or layerwise finite element calculationsA layerwise model and its dedicated 119862
∘ eight-node finite
element were specifically developed for interlaminar stressesanalysis in free edge problem Malekzadeh [24] developed ahigh accuracy and rapid convergence hybrid approach fortwo-dimensional static analyses of circular arches with dif-ferent boundary conditions The method essentially consistsof a layerwise theory used for the thickness direction inconjunction with differential quadrature method in the axialdirection
There have been very limited works to study the interlam-inar stresses subjected to the bendingmoment In the presentpaper by the use of Reddyrsquos LWT an analytical solutionis presented to evaluate interlaminar stresses in cross-plysymmetric angle-ply and general composite laminates underthe bending moment To commence with based on physicalarguments regarding the deformations of a long generally andother laminated composite plates an appropriate reducedelasticity displacement field is established The boundary-layer stresses within the laminate are obtained analyticallybased on Reddyrsquos LWT
2 Problem Formulation
21 Elasticity Displacement Field An Nth-layered compositeplate (with arbitrary lamination) under the bending momentis considered as shown in Figure 1 The coordinate system(119909 119910 119911) is located at the middle plane of the laminate thatis of thickness ℎ width 2119887 and length 2119886 and is assumed tobe long in the 119909 direction so that the strains away from theends (119909 = plusmn119886) of the laminate are functions of only 119910 and 119911
The integrations of the three-dimensional elasticitystrain-displacement relations [25] inside the kth layer of thelaminate will generate the most general form of displacementfield which can be shown to be [26]
119906(119896)
1
(119909 119910 119911) = 119861(119896)
4
119909119910 + 119861(119896)
6
119909119911 + 119861(119896)
2
119909 + 119906(119896)
(119910 119911)
119906(119896)
2
(119909 119910 119911) = minus119861(119896)
1
119909119911 + 119861(119896)
3
119909 minus1
2119861(119896)
4
1199092
+ V(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = 119861(119896)
1
119909119910 + 119861(119896)
5
119909 minus1
2119861(119896)
6
1199092
+ 119908(119896)
(119910 119911)
(1)
where 119906(119896)
1
119906(119896)2
and 119906(119896)
3
represent the displacement com-ponents of the material point (119909 119910 119911) in the 119909 119910 and 119911
International Journal of Engineering Mathematics 3
directions respectively To satisfy the displacement continu-ity conditions at the interfaces of the adjoining layers theintegration constants in (1) must be the same for all layerswithin the laminate Therefore the most general displace-ment field in the kth layer is shown
119906(119896)
1
(119909 119910 119911) = 1198614119909119910 + 119861
6119909119911 + 119861
2119909 + 119906(119896)
(119910 119911)
119906(119896)
2
(119909 119910 119911) = minus1198611119909119911 + 119861
3119909 minus
1
211986141199092
+ V(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = 1198611119909119910 + 119861
5119909 minus
1
211986161199092
+ 119908(119896)
(119910 119911)
(2)
If loading conditions at 119909 = minus119886 and 119886 are similar based onthe physical grounds the following conditions hold
119906(119896)
1
(119909 119910 119911) = minus119906(119896)
1
(minus119909 minus119910 119911)
119906(119896)
2
(119909 119910 119911) = minus119906(119896)
2
(minus119909 minus119910 119911)
119906(119896)
3
(119909 119910 119911) = 119906(119896)
3
(minus119909 minus119910 119911)
(3)
Upon imposing these restrictions on (1) it is readily seen thatthe constants 119861
4and 119861
5must vanish and the displacement
field in (1) is reduced to the following equations
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 1198616119909119911 + 119906
(119896)
(119910 119911) (4a)
119906(119896)
2
(119909 119910 119911) = minus1198611119909119911 + 119861
3119909 + V(119896)
(119910 119911) (4b)
119906(119896)
3
(119909 119910 119911) = 1198611119909119910 minus
1
211986161199092
+ 119908(119896)
(119910 119911) (4c)
Also by replacing 119906(119896)
(119910 119911) by minus1198613119910 + 119906
(119896)
(119910 119911) in (4a) itbecomes apparent that terms involving 119861
3in (4a)ndash(4c) can
be neglected since no strains are generated by such terms(these terms will correspond to an infinitesimal rigid-bodyrotation of the laminate about the z-axis in Figure 1) Thusthemost general formof the displacement field of an arbitrarylaminate is given by
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 1198616119909119911 + 119906
(119896)
(119910 119911) (5a)
119906(119896)
2
(119909 119910 119911) = minus1198611119909119911 + V
(119896)
(119910 119911) (5b)
119906(119896)
3
(119909 119910 119911) = 1198611119909119910 minus
1
211986161199092
+ 119908(119896)
(119910 119911) (5c)
The displacement field in (5a) (5b) and (5c) may be used inprinciple for computing the stress field in any composite lam-inate subjected to arbitrary combinations of self-equilibratingmechanical and uniform hygrothermal loads The termsinvolving 119861
1 1198612 and 119861
6in (5a) (5b) and (5c) demonstrate
certain global deformations that occurred in the laminate Onthe other hand the unknown functions appearing in (5a)(5b) and (5c) illustrate the local deformations They will beevaluated by LWT of Reddy that happened in a laminate
For cross-ply laminates subjected tomechanical loadingsbased on physical grounds the following restrictions hold(see Figure 1)
119906(119896)
1
(119909 119910 119911) = minus119906(119896)
1
(minus119909 119910 119911) (6a)
119906(119896)
2
(119909 119910 119911) = 119906(119896)
2
(minus119909 119910 119911) (6b)
Upon imposing these conditions on (5a) it is readily seen that119906(119896)
(119910 119911) = 0 Also it is concluded from (6b) and (5b) that1198611= 0 Thus for cross-ply laminates the most general form
of the displacement field is given
119906(119896)
1
(119909 119910 119911) = 1198616119909119911 + 119861
2119909
119906(119896)
2
(119909 119910 119911) = V(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = minus1
211986161199092
+ 119908(119896)
(119910 119911)
(7)
Also for symmetric laminates based on physical groundsthe following conditions must hold (see Figure 1)
119906(119896)
1
(119909 119910 119911) = 119906(119873+1minus119896)
1
(119909 119910 minus119911) (8a)
119906(119896)
2
(119909 119910 119911) = 119906(119873+1minus119896)
2
(119909 119910 minus119911) (8b)
119906(119896)
3
(119909 119910 119911) = minus 119906(119873+1minus119896)
3
(119909 119910 minus119911)
(119896 = 1 2 3 119873
2)
(8c)
Upon imposing these conditions on (5a) (5b) and (5c) it isfound that 119861
1= 1198616= 0 Thus for symmetric laminates the
most general form of displacement field is expressed by
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 119906(119896)
(119910 119911)
119906(119896)
2
(119909 119910 119911) = V(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = 119908(119896)
(119910 119911)
(9)
Finally for antisymmetric angle-ply laminateswith119873 lay-ers subjected tomechanical loadings the following conditionmust hold
119906(119896)
1
(119909 119910 119911) = 119906(119873+1minus119896)
1
(119909 minus119910 minus119911) (119896 = 1 2 3 119873
2)
(10)
Concluding from (10) and (5a) 1198616= 0 and therefore the
most general displacement field for such laminates arewrittenas
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 119906(119896)
(119910 119911)
119906(119896)
2
(119909 119910 119911) = minus1198611119909119911 + V
(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = 1198611119909119910 + 119908
(119896)
(119910 119911)
(11)
4 International Journal of Engineering Mathematics
The displacement fields in (7) (9) and (11) can be repre-sented in one place as
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 1205751198621198616119909119911 + 120575
119878119906(119896)
(119910 119911)
119906(119896)
2
(119909 119910 119911) = minus1205751198601198611119909119911 + V
(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = 1205751198601198611119909119910 minus
1
212057511986211986161199092
+ 119908(119896)
(119910 119911)
(12)
where 120575119860= 120575119878= 0 and 120575
119862= 1 for general cross-ply laminates
120575119860= 120575119862= 0 and 120575
119878= 1 for symmetric laminates 120575
119860= 120575119878= 1
and 120575119862= 0 for angle-ply laminates and 120575
119860= 120575119878= 120575119888= 1 for
general laminates
3 Layerwise Laminated Plate Theory of Reddy
In this section LWT is used for calculation of interlaminarstresses in arbitrary laminated composite plates with freeedges In LWT it is possible to replace the actual physicallayers to many mathematical layers [27] This can be doneby subdividing each physical layer through the thicknessto get the proper accuracy The theory assumes that thedisplacement components of a generic point in the laminateare given by [27]
1199061(119909 119910 119911) = 119906
119896(119909 119910) 120601
119896(119911)
1199062(119909 119910 119911) = V
119896(119909 119910) 120601
119896(119911)
1199063(119909 119910 119911) = 119908
119896(119909 119910) 120601
119896(119911)
119896 = 1 2 119873 + 1
(13)
It should be emphasized that a repeated index indicates sum-mation from 1 to119873 + 1 The functions 119906
119896(119909 119910) V
119896(119909 119910) and
119908119896(119909 119910) represent the displacements of the points initially
located at the kth plane of the laminate in the 119909 119910 and 119911
directions respectively The variable 119873 in (13) is the totalnumber of numerical layers introduced in any laminate Alsothe functions 120601
119896rsquos are the global approximation functions of
the thickness coordinate which are assumed here to be linear[27] This function expressed as
120601119896(119911) =
0 119911 le 119911119896minus1
1205952
119896minus1
(119911) 119911119896minus1
le 119911 le 119911119896
1205951
119896
(119911) 119911119896le 119911 le 119911
119896+1
0 119911 ge 119911119896+1
(119896 = 1 2 119873 + 1)
(14a)
where the local Lagrangian interpolation functions120595119895119896
(119911) (119895 =
1 2) related with the kth surface in the laminate are definedas
1205951
119896
(119911) =1
ℎ119896
(119911119896+1
minus 119911) 1205952
119896
(119911) =1
ℎ119896
(119911 minus 119911119896)
(14b)
where ℎ119896is the thickness of the kthmathematical layer Based
on the displacement field in (12) the displacement field ofLWT in (13) takes the following form
1199061(119909 119910 119911) = 120575
1198621198616119909119911 + 119861
2119909 + 120575119878119880119896(119910) 120601119896(119911)
1199062(119909 119910 119911) = minus120575
1198601198611119909119911 + 119881
119896(119910) 120601119896(119911)
1199063(119909 119910 119911) = 120575
1198601198611119909119910 minus
1
212057511986211986161199092
+119882119896(119910) 120601119896(119911)
119896 = 1 2 119873 + 1
(15)
It is noted that by the means of through-the-thicknesslinear interpolation functions the continuity of displacementcomponents through the thickness of laminate is identicallysatisfied On the other hand the transverse strain com-ponents remain discontinuous at the interfaces They willultimately emphasize the feasibility of having continuousinterlaminar stresses at the interfaces of adjoining layersby increasing the number of numerical layers through thephysical laminate Substituting (15) into the linear strain-displacement relations of elasticity [25] yields
120576119909= 1205751198621198616119911 + 1198612 120576
119910= 1198811015840
119896
120601119896 120576
119911= 1198821198961206011015840
119896
120574119910119911
= 1198811198961206011015840
119896
+1198821015840
119896
120601119896
120574119909119911
= 1205751198781198801198961206011015840
119896
+ 1205751198601198611119910 120574
119909119910= 1205751198781198801015840
119896
120601119896minus 1205751198601198611119911
(16)
where a prime in (16) denotes ordinary differentiation withrespect to a suitable independent variable (ie either 119910 or 119911)The three-dimensional constitutive law within the kth layer(with arbitrary fiber orientation) of the laminate may also beshown as [28]
(
(
120590119909
120590119910
120590119911
120590119910119911
120590119909119911
120590119909119910
)
)
(119896)
=
[[[[[[[[[
[
1198621111986212
11986213
0 0 11986216
11986212
11986222
11986223
0 0 11986226
11986213
11986223
11986233
0 0 11986236
0 0 0 11986244
11986245
0
0 0 0 11986245
11986255
0
11986216
11986226
11986236
0 0 11986266
]]]]]]]]]
]
(119896)
times(
(
120576119909
120576119910
120576119911
120574119910119911
120574119909119911
120574119909119910
)
)
(119896)
(17)
where [119862](119896) is the transformed (ie off axis) stiffness matrixof the kth layer By using the strain-displacement relations
International Journal of Engineering Mathematics 5
(16) in the principle of the minimum total potential energy[25] the equilibrium equations within LWT are found as
120575119880119896 120575119878(119876119896
119909
minus
d119872119896119909119910
d119910) = 0 119896 = 1 2 119873 + 1 (18a)
120575119881119896 119876119896119910
minus
d119872119896119910
d119910= 0 119896 = 1 2 119873 + 1 (18b)
120575119882119896 119873119896119911
minus
d119877119896119910
d119910= 0 119896 = 1 2 119873 + 1 (18c)
1205751198611 120575119860int
119887
minus119887
(119876119909119910 minus119872
119909119910) d119910 = 0 (19a)
1205751198612 int119887
minus119887
119873119909d119910 = 0 (19b)
1205751198616 120575119862int
119887
minus119887
119872119909d119910 = 119872
0 (19c)
Also the traction-free boundary conditions at the free edgesof the laminate are given as
119872119896
119910
= 119877119896
119910
= 120575119878119872119896
119909119910
= 0 at 119910 = plusmn119887 (119896 = 1 2 119873 + 1)
(20)
Equations (18a) (18b) and (18c) present 3(119873+1) local equilib-rium equations associated with119873+ 1 surface in the laminatewithin LWT Also (19a) (19b) and (19c) represent the globalequilibrium equation of a laminate The generalized stressandmoment resultants in (18a) (18b) (18c) (19a) (19b) (19c)and (20) are defined as
(119872119896
119910
119872119896
119909119910
119873119896
119911
) = int
ℎ2
minusℎ2
(120590119910120601119896 120590119909119910120601119896 1205901199111206011015840
) d119911 (21a)
(119876119896
119909
119876119896
119910
119877119896
119910
) = int
ℎ2
minusℎ2
(1205901199091199111206011015840
119896
1205901199101199111206011015840
119896
120590119910119911120601119896) d119911 (21b)
(119872119909 119873119909119872119909119910 119876119909) = int
ℎ2
minusℎ2
(120590119909119911 120590119909 120590119909119910119911 120590119909119911) d119911 (21c)
Substitution (16) into (17) and subsequently into (21a) (21b)and (21c) generates the following relations
(119872119896
119910
119872119896
119909119910
119873119896
119911
)
= 120575119878(119863119896119895
26
119863119896119895
66
119861119896119895
36
)1198801015840
119895
+ (119863119896119895
22
119863119896119895
26
119861119895119896
23
)1198811015840
119895
+ (119861119896119895
23
119861119896119895
36
119860119896119895
33
)119882119895minus 120575119860(119863119896
26
119863119896
66
119861119896
36
) 1198611
+ 120575119862(119863119896
12
119863119896
16
119861119896
13
) 1198616+ (119861119896
12
119861119896
16
119860119896
13
) 1198612
(22a)
(119876119896
119909
119876119896
119910
119877119896
119910
)
= 120575119878(119860119896119895
55
119860119896119895
45
119861119896119895
45
)119880119895+ (119860119896119895
45
119860119896119895
44
119861119896119895
44
)119881119895
+ (119861119895119896
45
119861119895119896
44
119863119896119895
44
)1198821015840
119895
minus 120575119860(119860119896
55
119860119896
45
119861119896
45
) 1198611119910
(22b)
(119872119910119872119909119910 119873119909)
= 120575119878(119863119896
16
119863119896
66
119861119896
16
)1198801015840
119895
+ (119863119896
12
119863119896
26
119861119896
12
)1198811015840
119895
+ (119861119896
13
119861119896
36
119860119896
13
)119882119895minus 120575119860(11986316 11986366 11986116) 1198611
+ 120575119862(11986111 11986116 11986011) 1198616+ (11986311 11986316 11986111) 1198612
(22c)
119876119909= 120575119878119860119896
55
119880119895+ 119860119896
45
119881119895+ 119861119896
45
1198821015840
119895
+ 120575119860119860551198611119910 (22d)
The explicit expressions for the laminate rigidities appearingin (22a) (22b) (22c) and (22d) in terms of 119862
119894rsquos are presented
in the Appendix Direct substitution of (22a) (22b) (22c)and (22d) into (18a) (18b) and (18c) provides the localdisplacement equilibrium equations within LWTThe resultsare expressed as
120575119880119896 120575119878(119863119896119895
66
11988010158401015840
119895
minus 119860119896119895
55
119880119895+ 119863119896119895
26
11988110158401015840
119895
minus 119860119896119895
45
119881119895+ (119861119896119895
36
minus 119861119895119896
45
)1198821015840
119895
) = 120575119860119860119896
55
1198611119910
119896 = 1 2 119873 + 1
(23a)
120575119881119896 120575119878119863119896119895
26
11988010158401015840
119895
minus 120575119878119860119896119895
45
119880119895+ 119863119896119895
22
11988110158401015840
119895
minus 119860119896119895
44
119881119895+ (119861119896119895
23
minus 119861119895119896
44
)1198821015840
119895
= 120575119860119860119896
45
1198611119910
119896 = 1 2 119873 + 1
(23b)
120575119882119896 120575119878(119861119896119895
45
minus 119861119895119896
36
)1198801015840
119895
minus (119861119896119895
44
minus 119861119895119896
23
)1198811015840
119895
+ 119863119896119895
44
11988210158401015840
119895
minus 119860119896119895
33
119882119895
= minus120575119860(119861119896
45
+ 119861119896
36
) 1198611+ 119860119896
13
1198612+ 120575119862119861119896
13
1198616
119896 = 1 2 119873 + 1
(23c)
In the same way upon substitution of (16) into (17) andthe subsequent results into (19a) (19b) and (19c) the globalequations (19a) (19b) and (19c) are found in terms ofdisplacement functions as follows
1205751198611 120575119860int
119887
minus119887
((120575119878119860119896
55
119880119895+ 119860119896
45
119881119895+ 119861119896
45
1198821015840
119895
) 119910
minus (120575119878119863119896
66
1198801015840
119895
+ 119863119896
26
1198811015840
119895
+ 119861119896
36
119882119895)
+ 120575119860(1198605511986111199102
+ 11986366) 1198611minus 119861161198612
minus120575119862119863161198616) d119910 = 0
(24a)
6 International Journal of Engineering Mathematics
1205751198612 int119887
minus119887
(120575119878119861119896
16
1198801015840
119895
+ 119861119896
12
1198811015840
119895
+ 119860119896
13
119882119895
minus 120575119860119861161198611+ 119860111198612+ 120575119862119861111198616) d119910 = 0
(24b)
1205751198616 120575119862int
119887
minus119887
(120575119878119863119896
16
1198801015840
119895
+ 119863119896
12
1198811015840
119895
+ 119861119896
13
119882119895
minus 120575119860119863161198611+ 119861111198612+ 120575119862119863111198616) d119910 = 119872
0
(24c)
where the extra laminate rigidities appearing in (24a) (24b)and (24c) are defined in the Appendix The system ofequations in (23a) (23b) and (23c) shows 3(119873 + 1) coupledordinary differential equations with constant coefficientswhich may be indicated in a matrix form as
[119872] 12057810158401015840
+ [119870] 120578 = [119871] 119861 sdot 119910 (25)
where
120578 = 119880119879
119881119879
119882119879
119879
119880 = 1198801 1198802 119880
119873+1119879
119881 = 1198811 1198812 119881
119873+1119879
119882 = 11988211198822 119882
119873+1119879
(26)
119861 = 1198611 1198612 1198616119879
119882119895= int
119910
119882119895d119910
(27)
The coefficient matrices [119872] [119870] and [119871] in (25) are dis-played in the Appendix Also from the conditions in (3) andthe displacement field in (23a) (23b) and (23c) it is observedthat the functions 119880
119895 119881119895 and119882
119895are all odd functions of the
independent variable 119910 It can be confirmed that the generalsolution of (25) may be presented as
120578 = [120595] [sinh (120582119910)] 119867 + [119870]minus1
[119871] 119861 sdot 119910 (28)
where [sinh(120582119910)] is a 3(119873 + 1) times 3(119873 + 1) diagonal matrixand
[sinh (120582119910)]
= diag (sinh (1205821119910) sinh (120582
2119910) sinh (120582
3(119873+1)119910))
(29)
Also [120595] and (1205822
1
1205822
2
1205822
3(119873+1)
) are the model matrixand eigenvalues of (minus[119872]
minus1
[119870]) respectively 119870 is anunknown vector representing 3(119873+1) integration constantsThe constants 119861
119895(119895 = 1 2 6)must be calculated within LWT
analysis So the boundary conditions in (20) are first imposedto found the vector 119870 in terms of the unknown parameters119861119895(119895 = 1 2 6) These constants are next calculated in terms
of the specific bending moment 1198720by satisfaction of the
global equilibrium conditions in (19a) (19b) and (19c)
0 01 02 03 04 05 06 07 08 09 1
0
10
20
30
minus40
minus30
minus20
minus10
120590
120590z120590xz
Goodsell and Pipes (2013)Goodsell and Pipes (2013)
yb
mdashPresent solutionmdashPresent solution
Figure 2 Interlaminar stresses along the 45∘
minus45∘ interface of
[45∘
minus45∘
]119904
laminate
Table 1 Engineering properties of unidirectional graphiteopoxy[28]
1198641
(GPa)1198642
= 1198643
(GPa)11986612
= 11986613
(GPa)11986623
(GPa) 12059212
= 12059213
12059223
132 108 565 338 024 059
4 Numerical Results and Discussions
In this part several numerical examples are shown for thedistribution of interlaminar stress All physical layers areassumed to be of equal thickness (=05mm)Themechanicalproperties of unidirectional graphiteepoxy T3005208 usedin this study are shown in Table 1 [28]
Also each physical ply is modeled as being made up of 12numerical layers within LWT (ie 119901 = 12) In addition thewidth thickness ratio (ie 2119887ℎ) is assumed to be equal to 10Furthermore the stress components are normalized as
120590119894119895=120590119894119895
1205900
(30)
where 1205900= 1198720119887ℎ2
Figure 2 shows the distribution of interlaminar normaland shear stresses along the width of [45∘minus45∘]
119904laminate
Good correspondence was found between the present resultsand the results obtained by Goodsell and Pipes [29] whichconfirms the accuracy of the present solution Figure 3 showsthe distribution of interlaminar stresses 120590
119911and 120590
119910119911along the
minus45∘
0∘ and 120590
119909119911along the 0
∘
90∘ interfaces of the general
[45∘
minus 45∘
0∘
90∘
30∘
minus 30∘
] laminate It is seen that theinterlaminar stresses show high stress gradient near the freeedge It is observed that the interlaminar stresses 120590
119911and 120590
119909119911
grow quickly near the free edge while being zero in the innerregion of the laminate Also the magnitude of the transverseshear stress 120590
119909119911is greater than that of transverse normal stress
120590119911 On the other hand 120590
119910119911rises toward the free edge and
decreases suddenly to zero at free edgeThe interlaminar normal stress 120590
119911along the 90∘0∘ inter-
face of the unsymmetric cross-ply [90∘
0∘
90∘
0∘
90∘
0∘
]
International Journal of Engineering Mathematics 7
0
0
01 02
02
03 04
04
05 06
06
07 08 09 1
minus02
minus04
minus06
minus08
120590
120590xz at z = 0
120590z at z = h6120590yz at z = h6
yb
Figure 3 Distribution of interlaminar stresses 120590119911
and 120590119910119911
alongthe minus45∘0∘ and 120590
119909119911
along the 0∘90∘ interfaces of the [45∘ minus 45∘0∘
90∘
30∘
minus30∘
] laminate
0 02 04 06 08 1yb
minus4
0
minus8
minus12
minus16
120590z
2bh = 502bh = 20
2bh = 102bh = 5
Figure 4 Distribution of the interlaminar normal stress 120590119911
alongthe 90∘0∘ interface of the laminate for various width-to-thicknessratios
laminate for various width-to-thickness ratios is demon-strated in Figure 4 It is observed that by decreasingthe width-to-thickness ratio the boundary-layer region canbe expanded towards the internal region of the laminate withits width being almost equal to the thickness of the laminateIt is seen that the magnitude of the interlaminar stress at thefree edge is not varied as the width-to-thickness ratio of thelaminate is changed In addition the highly localized natureof interlaminar stresses near and exactly at the free edges ofthe laminate is apparent
The distribution of interlaminar stresses along the0∘
90∘ and 90
∘
0∘ interfaces of the unsymmetric cross-ply
[0∘90∘0∘90∘] and [90∘0∘90∘0∘] laminates respectivelyare compared in Figure 5 It is seen that the maximuminterfacial value 120590
119911at the 0
∘
90∘ and 90
∘
0∘ interfaces take
place at the free edge Figure 6 shows the variation ofinterlaminar normal stress 120590
119911on through-the-thickness and
near the free edge of the angle-ply [45∘minus 45∘45∘minus 45∘]laminate as the free edge is approached It is observed that
120590z at z =h4120590z at z
120590yz
120590yz at z120590yz at z = h4
minus14minus12minus1
minus08minus06minus04minus02
0020406
0 02 04 06 08 1
= h4= h4
in [0∘90∘0∘90∘]
in [0∘90∘0∘90∘]
in [90∘0∘90∘0∘]in [90∘0∘90∘0∘]
yb
Figure 5 Distribution of interlaminar stresses along the 0∘
90∘
and 90∘
0∘ interfaces of the [0∘90∘0∘90∘] and [90∘0∘90∘0∘]
laminates respectively
minus1
minus05
0
05
1
minus200 minus150 minus100 minus50 0 50 100 150 200
zh
y = 094by = 096b
y = 099by = b
120590z
Figure 6 Variations of interlaminar normal stress 120590119911
through thethickness of the [45∘minus45∘45∘minus45∘] laminate for various width-to-thickness ratios
the maximum negative and positive values of 120590119911occur within
the top minus80∘ layer and the bottom 80
∘ layer at the free edge(ie 119910 = 119887) respectively It is also noticed that 120590
119911diminishes
away from the free edge as the interior region of the laminateis approached Moreover 120590
119911reduces by moving slightly away
from the free edge and its distribution becomes smootherThe variations of the interlaminar shear stress 120590
119910119911at 119910 =
119887 through the thickness of the [0∘
60∘
minus60∘
]119904laminate are
displayed in Figure 7 By increasing the number of numericallayers in each lamina 120590
119910119911becomes slightly closer to zero but
8 International Journal of Engineering Mathematics
minus15
minus1
minus05
0
05
1
15
minus20 minus10 0 10 20 30
zh
p = 20
p = 12
p = 8
120590yz
Figure 7 Variations of interlaminar shear stress 120590119910119911
on through-thickness of the [0∘60∘minus60∘]119904
laminate as a function of layer subdivisionnumber 119901
012
01
008
006
004
002
0
minus002
120590z
p = 30p = 20
p = 12p = 8
0 02 04 06 08 1
yb
Figure 8 Variations of interlaminar normal stress 120590119911
on through-thickness of the [minus15∘
90∘
90∘
minus15∘
] laminate as a function of layersubdivision number 119901
it never becomes zero It should be noted that increasing thenumber of subdivisions results in no convergence for 120590
119911and
120590119909119911
at interface-edge junction of two dissimilar layers Thenumerical values of these components (120590
119911and 120590
119909119911) continue
to grow as the number of sublayers increased Since thegeneralized stress resultants 119877119896
119910
instead of 120590119910119911
are forced todisappear at the free edge in LWT the numerical value of120590119910119911
may never become zero at the interface-edge intersection
(even by increasing the number of sublayers in each physicallayer)
The distribution of interlaminar normal stress 120590119911on
through thickness of the general [minus15∘90∘90∘minus15∘] lam-inate is displayed in Figure 8 It is noted that increasingthe number of numerical layers (119901) in each lamina has nosignificant effect on the values of the interlaminar stress 120590
119911
within the boundary-layer region of the laminate expect
International Journal of Engineering Mathematics 9
exactly at the free edge (ie 119910 = 119887) Furthermore theinterlaminar normal stress 120590
119911grows rapidly in the vicinity of
the free edge while being zero in the interior region of thelaminate
5 Conclusions
In the present paper analytical solutions are developed toanalyze the interlaminar stresses for different lay-up con-figurations in laminated composite plates subjected to thebending moment The solutions were obtained based onthe reduced elasticity displacement field for long laminatedplates It is found that the components of the displacementsfield are composed of two distinct parts signifying theglobal and local deformations within laminates The localdisplacement functions as well as the interlaminar stressesthrough the layers of the laminate were found by Reddyrsquoslayerwise theory (LWT)Thenumerical results based onLWTwere shown for the free-edge interlaminar stresses throughthe thickness and across the interfaces of various cross-plysymmetric angle-ply and general composite laminates
Appendix
The laminate rigidities in (22a) (22b) (22c) (22d) (24a)(24b) and (24c) are defined as
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
1206011015840
119895
1206011198961206011015840
119895
120601119896120601119895) d119911
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
120601119896 1206011015840
119896
119911 120601119896119911) d119911
(119896 119895 = 1 2 119873 + 1)
(119860119901119902 119861119901119902 119863119901119902) =
119873
sum
119894=1
int
119911119894+1
119911119894
119862(119894)
119901119902
(1 119911 1199112
) d119911
(A1)
which upon integration are presented in the following form
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
)
=
(minus
119862(119896minus1)
119901119902
ℎ119896minus1
minus
119862(119896minus1)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
6) if 119895 = 119896 minus 1
(
119862(119896minus1)
119901119902
ℎ119896minus1
+
119862(119896)
119901119902
ℎ119896
119862(119896minus1)
119901119902
2minus
119862(119896)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
3+
ℎ119896119862(119896)
119901119902
3) if 119895 = 119896
(minus
119862(119896)
119901119902
ℎ119896
119862(119896)
119901119902
2
ℎ119896119862(119896)
119901119902
6) if 119895 = 119896 + 1
(0 0 0) if 119895 lt 119896 minus 1 or 119895 gt 119896 + 1
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
)
=
(minus119862(1)
119901119902
ℎ1119862(1)
119901119902
2 119862(1)
119901119902
1199112
1
minus 1199112
2
2ℎ1
119862(1)
119901119902
ℎ1
[1199113
1
minus 1199113
2
3minus 1199112
1199112
1
minus 1199112
2
2]) if 119896 = 1
(minus119862(119896minus1)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2]) if 119896 = 119873 + 1
(119862(119896minus1)
119901119902
minus 119862(119896)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2+
ℎ119896119862(119896)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
+ 119862(119896)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2] +
119862(119896)
119901119902
ℎ119896
[1199113
119896
minus 1199113
119896+1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896+1
2]) if 1 lt 119896 lt 119873 + 1
(A2)
10 International Journal of Engineering Mathematics
Also
(119860119901119902 119861119901119902 119863119901119902)
=
119873
sum
119894=1
119862(119894)
119901119902
([119911119894+1
minus 119911119894] [
1199112
119894+1
minus 1199112
119894
2] [
1199113
119894+1
minus 1199113
119894
3])
(A3)
The coefficient matrices [119872] [119870] and [119871] appearing in(25) are given as
[119872] =[[
[
120575119878[11986366] 120575119878[11986326] 120575119878([11986136] minus [119861
45]119879
)
120575119878[11986326] [119863
22] [119861
23] minus [119861
44]119879
[0] [0] [11986344]
]]
]
[119870]=[
[
minus120575119878([11986055] + [120572]) minus120575
119878[11986045] [0]
minus120575119878[11986045] minus ([119860
44] + [120572]) [0]
120575119878([11986145]minus[11986136]119879
) [11986144]minus[11986123]119879
minus ([11986033]+[120572])
]
]
[119871] = [
[
12057511986011986055 0 0
12057511986011986045 0 0
minus120575119860(11986145 + 119861
36) 119860
13 12057511986211986113
]
]
(A4)
where [119860119901119902] [119861119901119902] and [119863
119901119902] are (119873 + 1) times (119873 + 1) square
matrices containing 119860119896119895119901119902 119861119896119895119901119902 and 119863
119896119895
119901119902 respectively and the
vectors 119860119901119902 119861119901119902 and 119861
119901119902 are (119873+1)times1 columnmatrices
containing 119860119896119901119902
119861119896119901119902
and 119861119896
119901119902
respectively Also [0] is (119873 +
1) times (119873 + 1) square zero and 0 is a zero vector with 119873 + 1
rows The artificial matrix [120572] is also an (119873 + 1) times (119873 + 1)
square matrix whose elements are given by
120572119896119895
= 120572int
ℎ2
minusℎ2
120601119896120601119895d119911 (A5)
with 120572 being a relatively small parameter in comparison withthe rigidity constants 119860119896119895
119901119902(119901119902 = 33 44 55) It is noted that
the insertion of [120572] in the matrix [119870] makes the eigenvaluesof the matrix (minus[119872]
minus1
[119870]) distinct
References
[1] T Kant and K Swaminathan ldquoEstimation of transverseinter-laminar stresses in laminated compositesmdasha selective reviewand survey of current developmentsrdquo Composite Structures vol49 no 1 pp 65ndash75 2000
[2] A H Puppo and H A Evensen ldquoInterlaminar shear ınlamınated composıtes under generalızed plane stressrdquo Journalof Composite Materials vol 4 pp 204ndash220 1970
[3] N J Pagano ldquoOn the calculatıon of ınterlamınar normal stressın composıte lamınaterdquo Journal of Composite Materials vol 8pp 65ndash81 1974
[4] P W Hsu and C T Herakovich ldquoEdge effects in angle-plycomposite laminatesrdquo Journal of CompositeMaterials vol 11 pp422ndash428 1977
[5] S Tang and A Levy ldquoBoundary layer theory 2 extension oflaminated finite striprdquo Journal of CompositeMaterials vol 9 no1 pp 42ndash52 1975
[6] R B Pipes andN J Pagano ldquoInterlaminar stresses in compositelaminates an approximate elasticity solutionrdquo Journal of AppliedMechanics vol 41 no 3 pp 668ndash672 1974
[7] N J Pagano ldquoStress fields in composite laminatesrdquo InternationalJournal of Solids and Structures vol 14 no 5 pp 385ndash400 1978
[8] S S Wang and I Choi ldquoBoundary-layer effects in composıtelaminates 1 free-edge stress singulaiıtiesrdquo Journal of AppliedMechanics vol V 49 no 3 pp 541ndash548 1982
[9] W L Yin ldquoFree-edge effects in anisotropic laminates underextension bending and twisting part I a stress-function-basedvariational approachrdquo Journal of Applied Mechanics vol 61 no2 pp 410ndash415 1994
[10] A S D Wang and F W Crossman ldquoSome new results on edgeeffect in symmetric composite laminatesrdquo Journal of CompositeMaterials vol 11 no 1 pp 92ndash106 1977
[11] J D Whitcomb I S Raju and J G Goree ldquoReliability ofthe finite element method for calculating free edge stresses incomposite laminatesrdquo Computers and Structures vol 15 no 1pp 23ndash37 1982
[12] G Davı ldquoStress fields in general composite laminatesrdquo AIAAJournal vol 34 no 12 pp 2604ndash2608 1996
[13] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT Part 1 derivationof finite element matricesrdquo International Journal for NumericalMethods in Engineering vol 55 no 2 pp 191ndash231 2002
[14] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT part 2 numericalimplementationsrdquo International Journal for Numerical Methodsin Engineering vol 55 no 3 pp 253ndash291 2002
[15] V-T Nguyen and J-F Caron ldquoFinite element analysis of free-edge stresses in composite laminates under mechanical anthermal loadingrdquo Composites Science and Technology vol 69no 1 pp 40ndash49 2009
[16] D H Robbins Jr and J N Reddy ldquoModelling of thick compos-ites using a layerwise laminate theoryrdquo International Journal forNumerical Methods in Engineering vol 36 no 4 pp 655ndash6771993
[17] C Mittelstedt and W Becker ldquoReddyrsquos layerwise laminate platetheory for the computation of elastic fields in the vicinity ofstraight free laminate edgesrdquoMaterials Science and EngineeringA vol 498 no 1-2 pp 76ndash80 2008
[18] W J Na Damage analysis of laminated composite beams underbending loads using the layer-wise theory [Dissertation thesis]Texas AampM University Texas Tex USA 2008
[19] T S Plagianakos and D A Saravanos ldquoHigher-order layerwiselaminate theory for the prediction of interlaminar shear stressesin thick composite and sandwich composite platesrdquo CompositeStructures vol 87 no 1 pp 23ndash35 2009
[20] H Ullah A R Harland T Lucas D Price and V V Sil-berschmidt ldquoFinite-element modelling of bending of CFRPlaminates multiple delaminationsrdquo Computational MaterialsScience vol 52 no 1 pp 147ndash156 2012
[21] F Helenon M R Wisnom S R Hallett and R S TraskldquoInvestigation into failure of laminated composite T-piecespecimens under bending loadingrdquo Composites A vol 54 pp182ndash189 2013
[22] C H Thai A J M Ferreira E Carrera and H Nguyen-XuanldquoIsogeometric analysis of laminated composite and sandwichplates using a layerwise deformation theoryrdquo Composite Struc-tures vol 104 pp 196ndash214 2013
International Journal of Engineering Mathematics 11
[23] N D Thai M DrsquoOttavio and J-F Caron ldquoBending analysis oflaminated and sandwich plates using a layer-wise stress modelrdquoComposite Structures vol 96 pp 135ndash142 2013
[24] PMalekzadeh ldquoA two-dimensional layerwise-differential quad-rature static analysis of thick laminated composite circulararchesrdquoAppliedMathematicalModelling vol 33 no 4 pp 1850ndash1861 2009
[25] Y C Fung and P Tong Classical and Computational SolidMechanics World Scientific New Jersey NJ USA 2001
[26] S G LekhnitskiiTheory of Elasticity of anAnisotropic BodyMirPublishers Moscow Russia 1981
[27] A Nosier R K Kapania and J N Reddy ldquoFree vibrationanalysis of laminated plates using a layerwise theoryrdquo AIAAJournal vol 31 no 12 pp 2335ndash2346 1993
[28] C T HerakovichMechanics of Fibrous Composites Wiley NewYork NY USA 1998
[29] O Goodsell and R B Pipes ldquoInterlaminar stresses in compositelaminates subjected to anticlastic bending deformationrdquo Journalof Applied Mechanics vol 80 no 4 pp 1ndash7 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
2 International Journal of Engineering Mathematics
y
z
x
a
a
2b
MO
MOh
Figure 1 Laminate geometry and coordinate system
by using the Reissner mixed variational theorem (RMVT)They compared the numerical results for interlaminar stressesin several finite-element models and elasticity theory withincomposite laminates and sandwich plates Nguyen andCaron[15] employed a multiparticle finite element method to studythe interlaminar stresses near the free edges of generalcomposite laminates under mechanical and thermal loadingRobbins and Reddy [16] used a displacement-based variablekinematic global-local finite elementmethodMittelstedt andBecker [17] utilizedReddyrsquos layerwise laminate plate theory tofind the closed-form analysis of free-edge effects in layeredplates of arbitrary nonorthotropic layups The approachconsists of the subdivision of the physical laminate layers intoan arbitrary number of mathematical layers through the platethickness Na [18] used a finite element model based on thelayerwise theory He employed the von Karman type nonlin-ear strains to analyze damage in laminated composite beamsIn his formulation the Heaviside step function is employedto express the discontinuous interlaminar displacement fieldat the delaminated interfaces Plagianakos and Saravanos [19]presented a higher-order layerwise theoretical frameworkwhich enables prediction of the static response of thick com-posite and sandwich composite plates Ullah et al [20] carriedout some experimental tests to characterize the behavior of awoven CFRP material under large-deflection bending Two-dimensional finite element (FE) models were implementedin the commercial code Abaqus They performed series ofsimulations to study the deformation behavior and damage inCFRP for cases of high-deflection bendingHelenon et al [21]presented an experimental and numerical investigation intofailure of T-shaped laminated composite structures Threeout-of-plane bending cases are studied They found thatvery high free-edge maximum principal transverse tensilestresses perpendicular to the fiber direction occur at thefailure locations Thai et al [22] indicated an isogeometricfinite element formulation for static free vibration and buck-ling analysis of laminated composite and sandwich platesTheir method allows removing shear correction factors andimproves the accuracy of transverse shear stresses Thai et al[23] investigated the behavior of laminated composites usingseveral high order or layerwise finite element calculationsA layerwise model and its dedicated 119862
∘ eight-node finite
element were specifically developed for interlaminar stressesanalysis in free edge problem Malekzadeh [24] developed ahigh accuracy and rapid convergence hybrid approach fortwo-dimensional static analyses of circular arches with dif-ferent boundary conditions The method essentially consistsof a layerwise theory used for the thickness direction inconjunction with differential quadrature method in the axialdirection
There have been very limited works to study the interlam-inar stresses subjected to the bendingmoment In the presentpaper by the use of Reddyrsquos LWT an analytical solutionis presented to evaluate interlaminar stresses in cross-plysymmetric angle-ply and general composite laminates underthe bending moment To commence with based on physicalarguments regarding the deformations of a long generally andother laminated composite plates an appropriate reducedelasticity displacement field is established The boundary-layer stresses within the laminate are obtained analyticallybased on Reddyrsquos LWT
2 Problem Formulation
21 Elasticity Displacement Field An Nth-layered compositeplate (with arbitrary lamination) under the bending momentis considered as shown in Figure 1 The coordinate system(119909 119910 119911) is located at the middle plane of the laminate thatis of thickness ℎ width 2119887 and length 2119886 and is assumed tobe long in the 119909 direction so that the strains away from theends (119909 = plusmn119886) of the laminate are functions of only 119910 and 119911
The integrations of the three-dimensional elasticitystrain-displacement relations [25] inside the kth layer of thelaminate will generate the most general form of displacementfield which can be shown to be [26]
119906(119896)
1
(119909 119910 119911) = 119861(119896)
4
119909119910 + 119861(119896)
6
119909119911 + 119861(119896)
2
119909 + 119906(119896)
(119910 119911)
119906(119896)
2
(119909 119910 119911) = minus119861(119896)
1
119909119911 + 119861(119896)
3
119909 minus1
2119861(119896)
4
1199092
+ V(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = 119861(119896)
1
119909119910 + 119861(119896)
5
119909 minus1
2119861(119896)
6
1199092
+ 119908(119896)
(119910 119911)
(1)
where 119906(119896)
1
119906(119896)2
and 119906(119896)
3
represent the displacement com-ponents of the material point (119909 119910 119911) in the 119909 119910 and 119911
International Journal of Engineering Mathematics 3
directions respectively To satisfy the displacement continu-ity conditions at the interfaces of the adjoining layers theintegration constants in (1) must be the same for all layerswithin the laminate Therefore the most general displace-ment field in the kth layer is shown
119906(119896)
1
(119909 119910 119911) = 1198614119909119910 + 119861
6119909119911 + 119861
2119909 + 119906(119896)
(119910 119911)
119906(119896)
2
(119909 119910 119911) = minus1198611119909119911 + 119861
3119909 minus
1
211986141199092
+ V(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = 1198611119909119910 + 119861
5119909 minus
1
211986161199092
+ 119908(119896)
(119910 119911)
(2)
If loading conditions at 119909 = minus119886 and 119886 are similar based onthe physical grounds the following conditions hold
119906(119896)
1
(119909 119910 119911) = minus119906(119896)
1
(minus119909 minus119910 119911)
119906(119896)
2
(119909 119910 119911) = minus119906(119896)
2
(minus119909 minus119910 119911)
119906(119896)
3
(119909 119910 119911) = 119906(119896)
3
(minus119909 minus119910 119911)
(3)
Upon imposing these restrictions on (1) it is readily seen thatthe constants 119861
4and 119861
5must vanish and the displacement
field in (1) is reduced to the following equations
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 1198616119909119911 + 119906
(119896)
(119910 119911) (4a)
119906(119896)
2
(119909 119910 119911) = minus1198611119909119911 + 119861
3119909 + V(119896)
(119910 119911) (4b)
119906(119896)
3
(119909 119910 119911) = 1198611119909119910 minus
1
211986161199092
+ 119908(119896)
(119910 119911) (4c)
Also by replacing 119906(119896)
(119910 119911) by minus1198613119910 + 119906
(119896)
(119910 119911) in (4a) itbecomes apparent that terms involving 119861
3in (4a)ndash(4c) can
be neglected since no strains are generated by such terms(these terms will correspond to an infinitesimal rigid-bodyrotation of the laminate about the z-axis in Figure 1) Thusthemost general formof the displacement field of an arbitrarylaminate is given by
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 1198616119909119911 + 119906
(119896)
(119910 119911) (5a)
119906(119896)
2
(119909 119910 119911) = minus1198611119909119911 + V
(119896)
(119910 119911) (5b)
119906(119896)
3
(119909 119910 119911) = 1198611119909119910 minus
1
211986161199092
+ 119908(119896)
(119910 119911) (5c)
The displacement field in (5a) (5b) and (5c) may be used inprinciple for computing the stress field in any composite lam-inate subjected to arbitrary combinations of self-equilibratingmechanical and uniform hygrothermal loads The termsinvolving 119861
1 1198612 and 119861
6in (5a) (5b) and (5c) demonstrate
certain global deformations that occurred in the laminate Onthe other hand the unknown functions appearing in (5a)(5b) and (5c) illustrate the local deformations They will beevaluated by LWT of Reddy that happened in a laminate
For cross-ply laminates subjected tomechanical loadingsbased on physical grounds the following restrictions hold(see Figure 1)
119906(119896)
1
(119909 119910 119911) = minus119906(119896)
1
(minus119909 119910 119911) (6a)
119906(119896)
2
(119909 119910 119911) = 119906(119896)
2
(minus119909 119910 119911) (6b)
Upon imposing these conditions on (5a) it is readily seen that119906(119896)
(119910 119911) = 0 Also it is concluded from (6b) and (5b) that1198611= 0 Thus for cross-ply laminates the most general form
of the displacement field is given
119906(119896)
1
(119909 119910 119911) = 1198616119909119911 + 119861
2119909
119906(119896)
2
(119909 119910 119911) = V(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = minus1
211986161199092
+ 119908(119896)
(119910 119911)
(7)
Also for symmetric laminates based on physical groundsthe following conditions must hold (see Figure 1)
119906(119896)
1
(119909 119910 119911) = 119906(119873+1minus119896)
1
(119909 119910 minus119911) (8a)
119906(119896)
2
(119909 119910 119911) = 119906(119873+1minus119896)
2
(119909 119910 minus119911) (8b)
119906(119896)
3
(119909 119910 119911) = minus 119906(119873+1minus119896)
3
(119909 119910 minus119911)
(119896 = 1 2 3 119873
2)
(8c)
Upon imposing these conditions on (5a) (5b) and (5c) it isfound that 119861
1= 1198616= 0 Thus for symmetric laminates the
most general form of displacement field is expressed by
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 119906(119896)
(119910 119911)
119906(119896)
2
(119909 119910 119911) = V(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = 119908(119896)
(119910 119911)
(9)
Finally for antisymmetric angle-ply laminateswith119873 lay-ers subjected tomechanical loadings the following conditionmust hold
119906(119896)
1
(119909 119910 119911) = 119906(119873+1minus119896)
1
(119909 minus119910 minus119911) (119896 = 1 2 3 119873
2)
(10)
Concluding from (10) and (5a) 1198616= 0 and therefore the
most general displacement field for such laminates arewrittenas
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 119906(119896)
(119910 119911)
119906(119896)
2
(119909 119910 119911) = minus1198611119909119911 + V
(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = 1198611119909119910 + 119908
(119896)
(119910 119911)
(11)
4 International Journal of Engineering Mathematics
The displacement fields in (7) (9) and (11) can be repre-sented in one place as
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 1205751198621198616119909119911 + 120575
119878119906(119896)
(119910 119911)
119906(119896)
2
(119909 119910 119911) = minus1205751198601198611119909119911 + V
(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = 1205751198601198611119909119910 minus
1
212057511986211986161199092
+ 119908(119896)
(119910 119911)
(12)
where 120575119860= 120575119878= 0 and 120575
119862= 1 for general cross-ply laminates
120575119860= 120575119862= 0 and 120575
119878= 1 for symmetric laminates 120575
119860= 120575119878= 1
and 120575119862= 0 for angle-ply laminates and 120575
119860= 120575119878= 120575119888= 1 for
general laminates
3 Layerwise Laminated Plate Theory of Reddy
In this section LWT is used for calculation of interlaminarstresses in arbitrary laminated composite plates with freeedges In LWT it is possible to replace the actual physicallayers to many mathematical layers [27] This can be doneby subdividing each physical layer through the thicknessto get the proper accuracy The theory assumes that thedisplacement components of a generic point in the laminateare given by [27]
1199061(119909 119910 119911) = 119906
119896(119909 119910) 120601
119896(119911)
1199062(119909 119910 119911) = V
119896(119909 119910) 120601
119896(119911)
1199063(119909 119910 119911) = 119908
119896(119909 119910) 120601
119896(119911)
119896 = 1 2 119873 + 1
(13)
It should be emphasized that a repeated index indicates sum-mation from 1 to119873 + 1 The functions 119906
119896(119909 119910) V
119896(119909 119910) and
119908119896(119909 119910) represent the displacements of the points initially
located at the kth plane of the laminate in the 119909 119910 and 119911
directions respectively The variable 119873 in (13) is the totalnumber of numerical layers introduced in any laminate Alsothe functions 120601
119896rsquos are the global approximation functions of
the thickness coordinate which are assumed here to be linear[27] This function expressed as
120601119896(119911) =
0 119911 le 119911119896minus1
1205952
119896minus1
(119911) 119911119896minus1
le 119911 le 119911119896
1205951
119896
(119911) 119911119896le 119911 le 119911
119896+1
0 119911 ge 119911119896+1
(119896 = 1 2 119873 + 1)
(14a)
where the local Lagrangian interpolation functions120595119895119896
(119911) (119895 =
1 2) related with the kth surface in the laminate are definedas
1205951
119896
(119911) =1
ℎ119896
(119911119896+1
minus 119911) 1205952
119896
(119911) =1
ℎ119896
(119911 minus 119911119896)
(14b)
where ℎ119896is the thickness of the kthmathematical layer Based
on the displacement field in (12) the displacement field ofLWT in (13) takes the following form
1199061(119909 119910 119911) = 120575
1198621198616119909119911 + 119861
2119909 + 120575119878119880119896(119910) 120601119896(119911)
1199062(119909 119910 119911) = minus120575
1198601198611119909119911 + 119881
119896(119910) 120601119896(119911)
1199063(119909 119910 119911) = 120575
1198601198611119909119910 minus
1
212057511986211986161199092
+119882119896(119910) 120601119896(119911)
119896 = 1 2 119873 + 1
(15)
It is noted that by the means of through-the-thicknesslinear interpolation functions the continuity of displacementcomponents through the thickness of laminate is identicallysatisfied On the other hand the transverse strain com-ponents remain discontinuous at the interfaces They willultimately emphasize the feasibility of having continuousinterlaminar stresses at the interfaces of adjoining layersby increasing the number of numerical layers through thephysical laminate Substituting (15) into the linear strain-displacement relations of elasticity [25] yields
120576119909= 1205751198621198616119911 + 1198612 120576
119910= 1198811015840
119896
120601119896 120576
119911= 1198821198961206011015840
119896
120574119910119911
= 1198811198961206011015840
119896
+1198821015840
119896
120601119896
120574119909119911
= 1205751198781198801198961206011015840
119896
+ 1205751198601198611119910 120574
119909119910= 1205751198781198801015840
119896
120601119896minus 1205751198601198611119911
(16)
where a prime in (16) denotes ordinary differentiation withrespect to a suitable independent variable (ie either 119910 or 119911)The three-dimensional constitutive law within the kth layer(with arbitrary fiber orientation) of the laminate may also beshown as [28]
(
(
120590119909
120590119910
120590119911
120590119910119911
120590119909119911
120590119909119910
)
)
(119896)
=
[[[[[[[[[
[
1198621111986212
11986213
0 0 11986216
11986212
11986222
11986223
0 0 11986226
11986213
11986223
11986233
0 0 11986236
0 0 0 11986244
11986245
0
0 0 0 11986245
11986255
0
11986216
11986226
11986236
0 0 11986266
]]]]]]]]]
]
(119896)
times(
(
120576119909
120576119910
120576119911
120574119910119911
120574119909119911
120574119909119910
)
)
(119896)
(17)
where [119862](119896) is the transformed (ie off axis) stiffness matrixof the kth layer By using the strain-displacement relations
International Journal of Engineering Mathematics 5
(16) in the principle of the minimum total potential energy[25] the equilibrium equations within LWT are found as
120575119880119896 120575119878(119876119896
119909
minus
d119872119896119909119910
d119910) = 0 119896 = 1 2 119873 + 1 (18a)
120575119881119896 119876119896119910
minus
d119872119896119910
d119910= 0 119896 = 1 2 119873 + 1 (18b)
120575119882119896 119873119896119911
minus
d119877119896119910
d119910= 0 119896 = 1 2 119873 + 1 (18c)
1205751198611 120575119860int
119887
minus119887
(119876119909119910 minus119872
119909119910) d119910 = 0 (19a)
1205751198612 int119887
minus119887
119873119909d119910 = 0 (19b)
1205751198616 120575119862int
119887
minus119887
119872119909d119910 = 119872
0 (19c)
Also the traction-free boundary conditions at the free edgesof the laminate are given as
119872119896
119910
= 119877119896
119910
= 120575119878119872119896
119909119910
= 0 at 119910 = plusmn119887 (119896 = 1 2 119873 + 1)
(20)
Equations (18a) (18b) and (18c) present 3(119873+1) local equilib-rium equations associated with119873+ 1 surface in the laminatewithin LWT Also (19a) (19b) and (19c) represent the globalequilibrium equation of a laminate The generalized stressandmoment resultants in (18a) (18b) (18c) (19a) (19b) (19c)and (20) are defined as
(119872119896
119910
119872119896
119909119910
119873119896
119911
) = int
ℎ2
minusℎ2
(120590119910120601119896 120590119909119910120601119896 1205901199111206011015840
) d119911 (21a)
(119876119896
119909
119876119896
119910
119877119896
119910
) = int
ℎ2
minusℎ2
(1205901199091199111206011015840
119896
1205901199101199111206011015840
119896
120590119910119911120601119896) d119911 (21b)
(119872119909 119873119909119872119909119910 119876119909) = int
ℎ2
minusℎ2
(120590119909119911 120590119909 120590119909119910119911 120590119909119911) d119911 (21c)
Substitution (16) into (17) and subsequently into (21a) (21b)and (21c) generates the following relations
(119872119896
119910
119872119896
119909119910
119873119896
119911
)
= 120575119878(119863119896119895
26
119863119896119895
66
119861119896119895
36
)1198801015840
119895
+ (119863119896119895
22
119863119896119895
26
119861119895119896
23
)1198811015840
119895
+ (119861119896119895
23
119861119896119895
36
119860119896119895
33
)119882119895minus 120575119860(119863119896
26
119863119896
66
119861119896
36
) 1198611
+ 120575119862(119863119896
12
119863119896
16
119861119896
13
) 1198616+ (119861119896
12
119861119896
16
119860119896
13
) 1198612
(22a)
(119876119896
119909
119876119896
119910
119877119896
119910
)
= 120575119878(119860119896119895
55
119860119896119895
45
119861119896119895
45
)119880119895+ (119860119896119895
45
119860119896119895
44
119861119896119895
44
)119881119895
+ (119861119895119896
45
119861119895119896
44
119863119896119895
44
)1198821015840
119895
minus 120575119860(119860119896
55
119860119896
45
119861119896
45
) 1198611119910
(22b)
(119872119910119872119909119910 119873119909)
= 120575119878(119863119896
16
119863119896
66
119861119896
16
)1198801015840
119895
+ (119863119896
12
119863119896
26
119861119896
12
)1198811015840
119895
+ (119861119896
13
119861119896
36
119860119896
13
)119882119895minus 120575119860(11986316 11986366 11986116) 1198611
+ 120575119862(11986111 11986116 11986011) 1198616+ (11986311 11986316 11986111) 1198612
(22c)
119876119909= 120575119878119860119896
55
119880119895+ 119860119896
45
119881119895+ 119861119896
45
1198821015840
119895
+ 120575119860119860551198611119910 (22d)
The explicit expressions for the laminate rigidities appearingin (22a) (22b) (22c) and (22d) in terms of 119862
119894rsquos are presented
in the Appendix Direct substitution of (22a) (22b) (22c)and (22d) into (18a) (18b) and (18c) provides the localdisplacement equilibrium equations within LWTThe resultsare expressed as
120575119880119896 120575119878(119863119896119895
66
11988010158401015840
119895
minus 119860119896119895
55
119880119895+ 119863119896119895
26
11988110158401015840
119895
minus 119860119896119895
45
119881119895+ (119861119896119895
36
minus 119861119895119896
45
)1198821015840
119895
) = 120575119860119860119896
55
1198611119910
119896 = 1 2 119873 + 1
(23a)
120575119881119896 120575119878119863119896119895
26
11988010158401015840
119895
minus 120575119878119860119896119895
45
119880119895+ 119863119896119895
22
11988110158401015840
119895
minus 119860119896119895
44
119881119895+ (119861119896119895
23
minus 119861119895119896
44
)1198821015840
119895
= 120575119860119860119896
45
1198611119910
119896 = 1 2 119873 + 1
(23b)
120575119882119896 120575119878(119861119896119895
45
minus 119861119895119896
36
)1198801015840
119895
minus (119861119896119895
44
minus 119861119895119896
23
)1198811015840
119895
+ 119863119896119895
44
11988210158401015840
119895
minus 119860119896119895
33
119882119895
= minus120575119860(119861119896
45
+ 119861119896
36
) 1198611+ 119860119896
13
1198612+ 120575119862119861119896
13
1198616
119896 = 1 2 119873 + 1
(23c)
In the same way upon substitution of (16) into (17) andthe subsequent results into (19a) (19b) and (19c) the globalequations (19a) (19b) and (19c) are found in terms ofdisplacement functions as follows
1205751198611 120575119860int
119887
minus119887
((120575119878119860119896
55
119880119895+ 119860119896
45
119881119895+ 119861119896
45
1198821015840
119895
) 119910
minus (120575119878119863119896
66
1198801015840
119895
+ 119863119896
26
1198811015840
119895
+ 119861119896
36
119882119895)
+ 120575119860(1198605511986111199102
+ 11986366) 1198611minus 119861161198612
minus120575119862119863161198616) d119910 = 0
(24a)
6 International Journal of Engineering Mathematics
1205751198612 int119887
minus119887
(120575119878119861119896
16
1198801015840
119895
+ 119861119896
12
1198811015840
119895
+ 119860119896
13
119882119895
minus 120575119860119861161198611+ 119860111198612+ 120575119862119861111198616) d119910 = 0
(24b)
1205751198616 120575119862int
119887
minus119887
(120575119878119863119896
16
1198801015840
119895
+ 119863119896
12
1198811015840
119895
+ 119861119896
13
119882119895
minus 120575119860119863161198611+ 119861111198612+ 120575119862119863111198616) d119910 = 119872
0
(24c)
where the extra laminate rigidities appearing in (24a) (24b)and (24c) are defined in the Appendix The system ofequations in (23a) (23b) and (23c) shows 3(119873 + 1) coupledordinary differential equations with constant coefficientswhich may be indicated in a matrix form as
[119872] 12057810158401015840
+ [119870] 120578 = [119871] 119861 sdot 119910 (25)
where
120578 = 119880119879
119881119879
119882119879
119879
119880 = 1198801 1198802 119880
119873+1119879
119881 = 1198811 1198812 119881
119873+1119879
119882 = 11988211198822 119882
119873+1119879
(26)
119861 = 1198611 1198612 1198616119879
119882119895= int
119910
119882119895d119910
(27)
The coefficient matrices [119872] [119870] and [119871] in (25) are dis-played in the Appendix Also from the conditions in (3) andthe displacement field in (23a) (23b) and (23c) it is observedthat the functions 119880
119895 119881119895 and119882
119895are all odd functions of the
independent variable 119910 It can be confirmed that the generalsolution of (25) may be presented as
120578 = [120595] [sinh (120582119910)] 119867 + [119870]minus1
[119871] 119861 sdot 119910 (28)
where [sinh(120582119910)] is a 3(119873 + 1) times 3(119873 + 1) diagonal matrixand
[sinh (120582119910)]
= diag (sinh (1205821119910) sinh (120582
2119910) sinh (120582
3(119873+1)119910))
(29)
Also [120595] and (1205822
1
1205822
2
1205822
3(119873+1)
) are the model matrixand eigenvalues of (minus[119872]
minus1
[119870]) respectively 119870 is anunknown vector representing 3(119873+1) integration constantsThe constants 119861
119895(119895 = 1 2 6)must be calculated within LWT
analysis So the boundary conditions in (20) are first imposedto found the vector 119870 in terms of the unknown parameters119861119895(119895 = 1 2 6) These constants are next calculated in terms
of the specific bending moment 1198720by satisfaction of the
global equilibrium conditions in (19a) (19b) and (19c)
0 01 02 03 04 05 06 07 08 09 1
0
10
20
30
minus40
minus30
minus20
minus10
120590
120590z120590xz
Goodsell and Pipes (2013)Goodsell and Pipes (2013)
yb
mdashPresent solutionmdashPresent solution
Figure 2 Interlaminar stresses along the 45∘
minus45∘ interface of
[45∘
minus45∘
]119904
laminate
Table 1 Engineering properties of unidirectional graphiteopoxy[28]
1198641
(GPa)1198642
= 1198643
(GPa)11986612
= 11986613
(GPa)11986623
(GPa) 12059212
= 12059213
12059223
132 108 565 338 024 059
4 Numerical Results and Discussions
In this part several numerical examples are shown for thedistribution of interlaminar stress All physical layers areassumed to be of equal thickness (=05mm)Themechanicalproperties of unidirectional graphiteepoxy T3005208 usedin this study are shown in Table 1 [28]
Also each physical ply is modeled as being made up of 12numerical layers within LWT (ie 119901 = 12) In addition thewidth thickness ratio (ie 2119887ℎ) is assumed to be equal to 10Furthermore the stress components are normalized as
120590119894119895=120590119894119895
1205900
(30)
where 1205900= 1198720119887ℎ2
Figure 2 shows the distribution of interlaminar normaland shear stresses along the width of [45∘minus45∘]
119904laminate
Good correspondence was found between the present resultsand the results obtained by Goodsell and Pipes [29] whichconfirms the accuracy of the present solution Figure 3 showsthe distribution of interlaminar stresses 120590
119911and 120590
119910119911along the
minus45∘
0∘ and 120590
119909119911along the 0
∘
90∘ interfaces of the general
[45∘
minus 45∘
0∘
90∘
30∘
minus 30∘
] laminate It is seen that theinterlaminar stresses show high stress gradient near the freeedge It is observed that the interlaminar stresses 120590
119911and 120590
119909119911
grow quickly near the free edge while being zero in the innerregion of the laminate Also the magnitude of the transverseshear stress 120590
119909119911is greater than that of transverse normal stress
120590119911 On the other hand 120590
119910119911rises toward the free edge and
decreases suddenly to zero at free edgeThe interlaminar normal stress 120590
119911along the 90∘0∘ inter-
face of the unsymmetric cross-ply [90∘
0∘
90∘
0∘
90∘
0∘
]
International Journal of Engineering Mathematics 7
0
0
01 02
02
03 04
04
05 06
06
07 08 09 1
minus02
minus04
minus06
minus08
120590
120590xz at z = 0
120590z at z = h6120590yz at z = h6
yb
Figure 3 Distribution of interlaminar stresses 120590119911
and 120590119910119911
alongthe minus45∘0∘ and 120590
119909119911
along the 0∘90∘ interfaces of the [45∘ minus 45∘0∘
90∘
30∘
minus30∘
] laminate
0 02 04 06 08 1yb
minus4
0
minus8
minus12
minus16
120590z
2bh = 502bh = 20
2bh = 102bh = 5
Figure 4 Distribution of the interlaminar normal stress 120590119911
alongthe 90∘0∘ interface of the laminate for various width-to-thicknessratios
laminate for various width-to-thickness ratios is demon-strated in Figure 4 It is observed that by decreasingthe width-to-thickness ratio the boundary-layer region canbe expanded towards the internal region of the laminate withits width being almost equal to the thickness of the laminateIt is seen that the magnitude of the interlaminar stress at thefree edge is not varied as the width-to-thickness ratio of thelaminate is changed In addition the highly localized natureof interlaminar stresses near and exactly at the free edges ofthe laminate is apparent
The distribution of interlaminar stresses along the0∘
90∘ and 90
∘
0∘ interfaces of the unsymmetric cross-ply
[0∘90∘0∘90∘] and [90∘0∘90∘0∘] laminates respectivelyare compared in Figure 5 It is seen that the maximuminterfacial value 120590
119911at the 0
∘
90∘ and 90
∘
0∘ interfaces take
place at the free edge Figure 6 shows the variation ofinterlaminar normal stress 120590
119911on through-the-thickness and
near the free edge of the angle-ply [45∘minus 45∘45∘minus 45∘]laminate as the free edge is approached It is observed that
120590z at z =h4120590z at z
120590yz
120590yz at z120590yz at z = h4
minus14minus12minus1
minus08minus06minus04minus02
0020406
0 02 04 06 08 1
= h4= h4
in [0∘90∘0∘90∘]
in [0∘90∘0∘90∘]
in [90∘0∘90∘0∘]in [90∘0∘90∘0∘]
yb
Figure 5 Distribution of interlaminar stresses along the 0∘
90∘
and 90∘
0∘ interfaces of the [0∘90∘0∘90∘] and [90∘0∘90∘0∘]
laminates respectively
minus1
minus05
0
05
1
minus200 minus150 minus100 minus50 0 50 100 150 200
zh
y = 094by = 096b
y = 099by = b
120590z
Figure 6 Variations of interlaminar normal stress 120590119911
through thethickness of the [45∘minus45∘45∘minus45∘] laminate for various width-to-thickness ratios
the maximum negative and positive values of 120590119911occur within
the top minus80∘ layer and the bottom 80
∘ layer at the free edge(ie 119910 = 119887) respectively It is also noticed that 120590
119911diminishes
away from the free edge as the interior region of the laminateis approached Moreover 120590
119911reduces by moving slightly away
from the free edge and its distribution becomes smootherThe variations of the interlaminar shear stress 120590
119910119911at 119910 =
119887 through the thickness of the [0∘
60∘
minus60∘
]119904laminate are
displayed in Figure 7 By increasing the number of numericallayers in each lamina 120590
119910119911becomes slightly closer to zero but
8 International Journal of Engineering Mathematics
minus15
minus1
minus05
0
05
1
15
minus20 minus10 0 10 20 30
zh
p = 20
p = 12
p = 8
120590yz
Figure 7 Variations of interlaminar shear stress 120590119910119911
on through-thickness of the [0∘60∘minus60∘]119904
laminate as a function of layer subdivisionnumber 119901
012
01
008
006
004
002
0
minus002
120590z
p = 30p = 20
p = 12p = 8
0 02 04 06 08 1
yb
Figure 8 Variations of interlaminar normal stress 120590119911
on through-thickness of the [minus15∘
90∘
90∘
minus15∘
] laminate as a function of layersubdivision number 119901
it never becomes zero It should be noted that increasing thenumber of subdivisions results in no convergence for 120590
119911and
120590119909119911
at interface-edge junction of two dissimilar layers Thenumerical values of these components (120590
119911and 120590
119909119911) continue
to grow as the number of sublayers increased Since thegeneralized stress resultants 119877119896
119910
instead of 120590119910119911
are forced todisappear at the free edge in LWT the numerical value of120590119910119911
may never become zero at the interface-edge intersection
(even by increasing the number of sublayers in each physicallayer)
The distribution of interlaminar normal stress 120590119911on
through thickness of the general [minus15∘90∘90∘minus15∘] lam-inate is displayed in Figure 8 It is noted that increasingthe number of numerical layers (119901) in each lamina has nosignificant effect on the values of the interlaminar stress 120590
119911
within the boundary-layer region of the laminate expect
International Journal of Engineering Mathematics 9
exactly at the free edge (ie 119910 = 119887) Furthermore theinterlaminar normal stress 120590
119911grows rapidly in the vicinity of
the free edge while being zero in the interior region of thelaminate
5 Conclusions
In the present paper analytical solutions are developed toanalyze the interlaminar stresses for different lay-up con-figurations in laminated composite plates subjected to thebending moment The solutions were obtained based onthe reduced elasticity displacement field for long laminatedplates It is found that the components of the displacementsfield are composed of two distinct parts signifying theglobal and local deformations within laminates The localdisplacement functions as well as the interlaminar stressesthrough the layers of the laminate were found by Reddyrsquoslayerwise theory (LWT)Thenumerical results based onLWTwere shown for the free-edge interlaminar stresses throughthe thickness and across the interfaces of various cross-plysymmetric angle-ply and general composite laminates
Appendix
The laminate rigidities in (22a) (22b) (22c) (22d) (24a)(24b) and (24c) are defined as
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
1206011015840
119895
1206011198961206011015840
119895
120601119896120601119895) d119911
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
120601119896 1206011015840
119896
119911 120601119896119911) d119911
(119896 119895 = 1 2 119873 + 1)
(119860119901119902 119861119901119902 119863119901119902) =
119873
sum
119894=1
int
119911119894+1
119911119894
119862(119894)
119901119902
(1 119911 1199112
) d119911
(A1)
which upon integration are presented in the following form
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
)
=
(minus
119862(119896minus1)
119901119902
ℎ119896minus1
minus
119862(119896minus1)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
6) if 119895 = 119896 minus 1
(
119862(119896minus1)
119901119902
ℎ119896minus1
+
119862(119896)
119901119902
ℎ119896
119862(119896minus1)
119901119902
2minus
119862(119896)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
3+
ℎ119896119862(119896)
119901119902
3) if 119895 = 119896
(minus
119862(119896)
119901119902
ℎ119896
119862(119896)
119901119902
2
ℎ119896119862(119896)
119901119902
6) if 119895 = 119896 + 1
(0 0 0) if 119895 lt 119896 minus 1 or 119895 gt 119896 + 1
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
)
=
(minus119862(1)
119901119902
ℎ1119862(1)
119901119902
2 119862(1)
119901119902
1199112
1
minus 1199112
2
2ℎ1
119862(1)
119901119902
ℎ1
[1199113
1
minus 1199113
2
3minus 1199112
1199112
1
minus 1199112
2
2]) if 119896 = 1
(minus119862(119896minus1)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2]) if 119896 = 119873 + 1
(119862(119896minus1)
119901119902
minus 119862(119896)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2+
ℎ119896119862(119896)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
+ 119862(119896)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2] +
119862(119896)
119901119902
ℎ119896
[1199113
119896
minus 1199113
119896+1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896+1
2]) if 1 lt 119896 lt 119873 + 1
(A2)
10 International Journal of Engineering Mathematics
Also
(119860119901119902 119861119901119902 119863119901119902)
=
119873
sum
119894=1
119862(119894)
119901119902
([119911119894+1
minus 119911119894] [
1199112
119894+1
minus 1199112
119894
2] [
1199113
119894+1
minus 1199113
119894
3])
(A3)
The coefficient matrices [119872] [119870] and [119871] appearing in(25) are given as
[119872] =[[
[
120575119878[11986366] 120575119878[11986326] 120575119878([11986136] minus [119861
45]119879
)
120575119878[11986326] [119863
22] [119861
23] minus [119861
44]119879
[0] [0] [11986344]
]]
]
[119870]=[
[
minus120575119878([11986055] + [120572]) minus120575
119878[11986045] [0]
minus120575119878[11986045] minus ([119860
44] + [120572]) [0]
120575119878([11986145]minus[11986136]119879
) [11986144]minus[11986123]119879
minus ([11986033]+[120572])
]
]
[119871] = [
[
12057511986011986055 0 0
12057511986011986045 0 0
minus120575119860(11986145 + 119861
36) 119860
13 12057511986211986113
]
]
(A4)
where [119860119901119902] [119861119901119902] and [119863
119901119902] are (119873 + 1) times (119873 + 1) square
matrices containing 119860119896119895119901119902 119861119896119895119901119902 and 119863
119896119895
119901119902 respectively and the
vectors 119860119901119902 119861119901119902 and 119861
119901119902 are (119873+1)times1 columnmatrices
containing 119860119896119901119902
119861119896119901119902
and 119861119896
119901119902
respectively Also [0] is (119873 +
1) times (119873 + 1) square zero and 0 is a zero vector with 119873 + 1
rows The artificial matrix [120572] is also an (119873 + 1) times (119873 + 1)
square matrix whose elements are given by
120572119896119895
= 120572int
ℎ2
minusℎ2
120601119896120601119895d119911 (A5)
with 120572 being a relatively small parameter in comparison withthe rigidity constants 119860119896119895
119901119902(119901119902 = 33 44 55) It is noted that
the insertion of [120572] in the matrix [119870] makes the eigenvaluesof the matrix (minus[119872]
minus1
[119870]) distinct
References
[1] T Kant and K Swaminathan ldquoEstimation of transverseinter-laminar stresses in laminated compositesmdasha selective reviewand survey of current developmentsrdquo Composite Structures vol49 no 1 pp 65ndash75 2000
[2] A H Puppo and H A Evensen ldquoInterlaminar shear ınlamınated composıtes under generalızed plane stressrdquo Journalof Composite Materials vol 4 pp 204ndash220 1970
[3] N J Pagano ldquoOn the calculatıon of ınterlamınar normal stressın composıte lamınaterdquo Journal of Composite Materials vol 8pp 65ndash81 1974
[4] P W Hsu and C T Herakovich ldquoEdge effects in angle-plycomposite laminatesrdquo Journal of CompositeMaterials vol 11 pp422ndash428 1977
[5] S Tang and A Levy ldquoBoundary layer theory 2 extension oflaminated finite striprdquo Journal of CompositeMaterials vol 9 no1 pp 42ndash52 1975
[6] R B Pipes andN J Pagano ldquoInterlaminar stresses in compositelaminates an approximate elasticity solutionrdquo Journal of AppliedMechanics vol 41 no 3 pp 668ndash672 1974
[7] N J Pagano ldquoStress fields in composite laminatesrdquo InternationalJournal of Solids and Structures vol 14 no 5 pp 385ndash400 1978
[8] S S Wang and I Choi ldquoBoundary-layer effects in composıtelaminates 1 free-edge stress singulaiıtiesrdquo Journal of AppliedMechanics vol V 49 no 3 pp 541ndash548 1982
[9] W L Yin ldquoFree-edge effects in anisotropic laminates underextension bending and twisting part I a stress-function-basedvariational approachrdquo Journal of Applied Mechanics vol 61 no2 pp 410ndash415 1994
[10] A S D Wang and F W Crossman ldquoSome new results on edgeeffect in symmetric composite laminatesrdquo Journal of CompositeMaterials vol 11 no 1 pp 92ndash106 1977
[11] J D Whitcomb I S Raju and J G Goree ldquoReliability ofthe finite element method for calculating free edge stresses incomposite laminatesrdquo Computers and Structures vol 15 no 1pp 23ndash37 1982
[12] G Davı ldquoStress fields in general composite laminatesrdquo AIAAJournal vol 34 no 12 pp 2604ndash2608 1996
[13] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT Part 1 derivationof finite element matricesrdquo International Journal for NumericalMethods in Engineering vol 55 no 2 pp 191ndash231 2002
[14] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT part 2 numericalimplementationsrdquo International Journal for Numerical Methodsin Engineering vol 55 no 3 pp 253ndash291 2002
[15] V-T Nguyen and J-F Caron ldquoFinite element analysis of free-edge stresses in composite laminates under mechanical anthermal loadingrdquo Composites Science and Technology vol 69no 1 pp 40ndash49 2009
[16] D H Robbins Jr and J N Reddy ldquoModelling of thick compos-ites using a layerwise laminate theoryrdquo International Journal forNumerical Methods in Engineering vol 36 no 4 pp 655ndash6771993
[17] C Mittelstedt and W Becker ldquoReddyrsquos layerwise laminate platetheory for the computation of elastic fields in the vicinity ofstraight free laminate edgesrdquoMaterials Science and EngineeringA vol 498 no 1-2 pp 76ndash80 2008
[18] W J Na Damage analysis of laminated composite beams underbending loads using the layer-wise theory [Dissertation thesis]Texas AampM University Texas Tex USA 2008
[19] T S Plagianakos and D A Saravanos ldquoHigher-order layerwiselaminate theory for the prediction of interlaminar shear stressesin thick composite and sandwich composite platesrdquo CompositeStructures vol 87 no 1 pp 23ndash35 2009
[20] H Ullah A R Harland T Lucas D Price and V V Sil-berschmidt ldquoFinite-element modelling of bending of CFRPlaminates multiple delaminationsrdquo Computational MaterialsScience vol 52 no 1 pp 147ndash156 2012
[21] F Helenon M R Wisnom S R Hallett and R S TraskldquoInvestigation into failure of laminated composite T-piecespecimens under bending loadingrdquo Composites A vol 54 pp182ndash189 2013
[22] C H Thai A J M Ferreira E Carrera and H Nguyen-XuanldquoIsogeometric analysis of laminated composite and sandwichplates using a layerwise deformation theoryrdquo Composite Struc-tures vol 104 pp 196ndash214 2013
International Journal of Engineering Mathematics 11
[23] N D Thai M DrsquoOttavio and J-F Caron ldquoBending analysis oflaminated and sandwich plates using a layer-wise stress modelrdquoComposite Structures vol 96 pp 135ndash142 2013
[24] PMalekzadeh ldquoA two-dimensional layerwise-differential quad-rature static analysis of thick laminated composite circulararchesrdquoAppliedMathematicalModelling vol 33 no 4 pp 1850ndash1861 2009
[25] Y C Fung and P Tong Classical and Computational SolidMechanics World Scientific New Jersey NJ USA 2001
[26] S G LekhnitskiiTheory of Elasticity of anAnisotropic BodyMirPublishers Moscow Russia 1981
[27] A Nosier R K Kapania and J N Reddy ldquoFree vibrationanalysis of laminated plates using a layerwise theoryrdquo AIAAJournal vol 31 no 12 pp 2335ndash2346 1993
[28] C T HerakovichMechanics of Fibrous Composites Wiley NewYork NY USA 1998
[29] O Goodsell and R B Pipes ldquoInterlaminar stresses in compositelaminates subjected to anticlastic bending deformationrdquo Journalof Applied Mechanics vol 80 no 4 pp 1ndash7 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
International Journal of Engineering Mathematics 3
directions respectively To satisfy the displacement continu-ity conditions at the interfaces of the adjoining layers theintegration constants in (1) must be the same for all layerswithin the laminate Therefore the most general displace-ment field in the kth layer is shown
119906(119896)
1
(119909 119910 119911) = 1198614119909119910 + 119861
6119909119911 + 119861
2119909 + 119906(119896)
(119910 119911)
119906(119896)
2
(119909 119910 119911) = minus1198611119909119911 + 119861
3119909 minus
1
211986141199092
+ V(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = 1198611119909119910 + 119861
5119909 minus
1
211986161199092
+ 119908(119896)
(119910 119911)
(2)
If loading conditions at 119909 = minus119886 and 119886 are similar based onthe physical grounds the following conditions hold
119906(119896)
1
(119909 119910 119911) = minus119906(119896)
1
(minus119909 minus119910 119911)
119906(119896)
2
(119909 119910 119911) = minus119906(119896)
2
(minus119909 minus119910 119911)
119906(119896)
3
(119909 119910 119911) = 119906(119896)
3
(minus119909 minus119910 119911)
(3)
Upon imposing these restrictions on (1) it is readily seen thatthe constants 119861
4and 119861
5must vanish and the displacement
field in (1) is reduced to the following equations
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 1198616119909119911 + 119906
(119896)
(119910 119911) (4a)
119906(119896)
2
(119909 119910 119911) = minus1198611119909119911 + 119861
3119909 + V(119896)
(119910 119911) (4b)
119906(119896)
3
(119909 119910 119911) = 1198611119909119910 minus
1
211986161199092
+ 119908(119896)
(119910 119911) (4c)
Also by replacing 119906(119896)
(119910 119911) by minus1198613119910 + 119906
(119896)
(119910 119911) in (4a) itbecomes apparent that terms involving 119861
3in (4a)ndash(4c) can
be neglected since no strains are generated by such terms(these terms will correspond to an infinitesimal rigid-bodyrotation of the laminate about the z-axis in Figure 1) Thusthemost general formof the displacement field of an arbitrarylaminate is given by
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 1198616119909119911 + 119906
(119896)
(119910 119911) (5a)
119906(119896)
2
(119909 119910 119911) = minus1198611119909119911 + V
(119896)
(119910 119911) (5b)
119906(119896)
3
(119909 119910 119911) = 1198611119909119910 minus
1
211986161199092
+ 119908(119896)
(119910 119911) (5c)
The displacement field in (5a) (5b) and (5c) may be used inprinciple for computing the stress field in any composite lam-inate subjected to arbitrary combinations of self-equilibratingmechanical and uniform hygrothermal loads The termsinvolving 119861
1 1198612 and 119861
6in (5a) (5b) and (5c) demonstrate
certain global deformations that occurred in the laminate Onthe other hand the unknown functions appearing in (5a)(5b) and (5c) illustrate the local deformations They will beevaluated by LWT of Reddy that happened in a laminate
For cross-ply laminates subjected tomechanical loadingsbased on physical grounds the following restrictions hold(see Figure 1)
119906(119896)
1
(119909 119910 119911) = minus119906(119896)
1
(minus119909 119910 119911) (6a)
119906(119896)
2
(119909 119910 119911) = 119906(119896)
2
(minus119909 119910 119911) (6b)
Upon imposing these conditions on (5a) it is readily seen that119906(119896)
(119910 119911) = 0 Also it is concluded from (6b) and (5b) that1198611= 0 Thus for cross-ply laminates the most general form
of the displacement field is given
119906(119896)
1
(119909 119910 119911) = 1198616119909119911 + 119861
2119909
119906(119896)
2
(119909 119910 119911) = V(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = minus1
211986161199092
+ 119908(119896)
(119910 119911)
(7)
Also for symmetric laminates based on physical groundsthe following conditions must hold (see Figure 1)
119906(119896)
1
(119909 119910 119911) = 119906(119873+1minus119896)
1
(119909 119910 minus119911) (8a)
119906(119896)
2
(119909 119910 119911) = 119906(119873+1minus119896)
2
(119909 119910 minus119911) (8b)
119906(119896)
3
(119909 119910 119911) = minus 119906(119873+1minus119896)
3
(119909 119910 minus119911)
(119896 = 1 2 3 119873
2)
(8c)
Upon imposing these conditions on (5a) (5b) and (5c) it isfound that 119861
1= 1198616= 0 Thus for symmetric laminates the
most general form of displacement field is expressed by
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 119906(119896)
(119910 119911)
119906(119896)
2
(119909 119910 119911) = V(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = 119908(119896)
(119910 119911)
(9)
Finally for antisymmetric angle-ply laminateswith119873 lay-ers subjected tomechanical loadings the following conditionmust hold
119906(119896)
1
(119909 119910 119911) = 119906(119873+1minus119896)
1
(119909 minus119910 minus119911) (119896 = 1 2 3 119873
2)
(10)
Concluding from (10) and (5a) 1198616= 0 and therefore the
most general displacement field for such laminates arewrittenas
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 119906(119896)
(119910 119911)
119906(119896)
2
(119909 119910 119911) = minus1198611119909119911 + V
(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = 1198611119909119910 + 119908
(119896)
(119910 119911)
(11)
4 International Journal of Engineering Mathematics
The displacement fields in (7) (9) and (11) can be repre-sented in one place as
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 1205751198621198616119909119911 + 120575
119878119906(119896)
(119910 119911)
119906(119896)
2
(119909 119910 119911) = minus1205751198601198611119909119911 + V
(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = 1205751198601198611119909119910 minus
1
212057511986211986161199092
+ 119908(119896)
(119910 119911)
(12)
where 120575119860= 120575119878= 0 and 120575
119862= 1 for general cross-ply laminates
120575119860= 120575119862= 0 and 120575
119878= 1 for symmetric laminates 120575
119860= 120575119878= 1
and 120575119862= 0 for angle-ply laminates and 120575
119860= 120575119878= 120575119888= 1 for
general laminates
3 Layerwise Laminated Plate Theory of Reddy
In this section LWT is used for calculation of interlaminarstresses in arbitrary laminated composite plates with freeedges In LWT it is possible to replace the actual physicallayers to many mathematical layers [27] This can be doneby subdividing each physical layer through the thicknessto get the proper accuracy The theory assumes that thedisplacement components of a generic point in the laminateare given by [27]
1199061(119909 119910 119911) = 119906
119896(119909 119910) 120601
119896(119911)
1199062(119909 119910 119911) = V
119896(119909 119910) 120601
119896(119911)
1199063(119909 119910 119911) = 119908
119896(119909 119910) 120601
119896(119911)
119896 = 1 2 119873 + 1
(13)
It should be emphasized that a repeated index indicates sum-mation from 1 to119873 + 1 The functions 119906
119896(119909 119910) V
119896(119909 119910) and
119908119896(119909 119910) represent the displacements of the points initially
located at the kth plane of the laminate in the 119909 119910 and 119911
directions respectively The variable 119873 in (13) is the totalnumber of numerical layers introduced in any laminate Alsothe functions 120601
119896rsquos are the global approximation functions of
the thickness coordinate which are assumed here to be linear[27] This function expressed as
120601119896(119911) =
0 119911 le 119911119896minus1
1205952
119896minus1
(119911) 119911119896minus1
le 119911 le 119911119896
1205951
119896
(119911) 119911119896le 119911 le 119911
119896+1
0 119911 ge 119911119896+1
(119896 = 1 2 119873 + 1)
(14a)
where the local Lagrangian interpolation functions120595119895119896
(119911) (119895 =
1 2) related with the kth surface in the laminate are definedas
1205951
119896
(119911) =1
ℎ119896
(119911119896+1
minus 119911) 1205952
119896
(119911) =1
ℎ119896
(119911 minus 119911119896)
(14b)
where ℎ119896is the thickness of the kthmathematical layer Based
on the displacement field in (12) the displacement field ofLWT in (13) takes the following form
1199061(119909 119910 119911) = 120575
1198621198616119909119911 + 119861
2119909 + 120575119878119880119896(119910) 120601119896(119911)
1199062(119909 119910 119911) = minus120575
1198601198611119909119911 + 119881
119896(119910) 120601119896(119911)
1199063(119909 119910 119911) = 120575
1198601198611119909119910 minus
1
212057511986211986161199092
+119882119896(119910) 120601119896(119911)
119896 = 1 2 119873 + 1
(15)
It is noted that by the means of through-the-thicknesslinear interpolation functions the continuity of displacementcomponents through the thickness of laminate is identicallysatisfied On the other hand the transverse strain com-ponents remain discontinuous at the interfaces They willultimately emphasize the feasibility of having continuousinterlaminar stresses at the interfaces of adjoining layersby increasing the number of numerical layers through thephysical laminate Substituting (15) into the linear strain-displacement relations of elasticity [25] yields
120576119909= 1205751198621198616119911 + 1198612 120576
119910= 1198811015840
119896
120601119896 120576
119911= 1198821198961206011015840
119896
120574119910119911
= 1198811198961206011015840
119896
+1198821015840
119896
120601119896
120574119909119911
= 1205751198781198801198961206011015840
119896
+ 1205751198601198611119910 120574
119909119910= 1205751198781198801015840
119896
120601119896minus 1205751198601198611119911
(16)
where a prime in (16) denotes ordinary differentiation withrespect to a suitable independent variable (ie either 119910 or 119911)The three-dimensional constitutive law within the kth layer(with arbitrary fiber orientation) of the laminate may also beshown as [28]
(
(
120590119909
120590119910
120590119911
120590119910119911
120590119909119911
120590119909119910
)
)
(119896)
=
[[[[[[[[[
[
1198621111986212
11986213
0 0 11986216
11986212
11986222
11986223
0 0 11986226
11986213
11986223
11986233
0 0 11986236
0 0 0 11986244
11986245
0
0 0 0 11986245
11986255
0
11986216
11986226
11986236
0 0 11986266
]]]]]]]]]
]
(119896)
times(
(
120576119909
120576119910
120576119911
120574119910119911
120574119909119911
120574119909119910
)
)
(119896)
(17)
where [119862](119896) is the transformed (ie off axis) stiffness matrixof the kth layer By using the strain-displacement relations
International Journal of Engineering Mathematics 5
(16) in the principle of the minimum total potential energy[25] the equilibrium equations within LWT are found as
120575119880119896 120575119878(119876119896
119909
minus
d119872119896119909119910
d119910) = 0 119896 = 1 2 119873 + 1 (18a)
120575119881119896 119876119896119910
minus
d119872119896119910
d119910= 0 119896 = 1 2 119873 + 1 (18b)
120575119882119896 119873119896119911
minus
d119877119896119910
d119910= 0 119896 = 1 2 119873 + 1 (18c)
1205751198611 120575119860int
119887
minus119887
(119876119909119910 minus119872
119909119910) d119910 = 0 (19a)
1205751198612 int119887
minus119887
119873119909d119910 = 0 (19b)
1205751198616 120575119862int
119887
minus119887
119872119909d119910 = 119872
0 (19c)
Also the traction-free boundary conditions at the free edgesof the laminate are given as
119872119896
119910
= 119877119896
119910
= 120575119878119872119896
119909119910
= 0 at 119910 = plusmn119887 (119896 = 1 2 119873 + 1)
(20)
Equations (18a) (18b) and (18c) present 3(119873+1) local equilib-rium equations associated with119873+ 1 surface in the laminatewithin LWT Also (19a) (19b) and (19c) represent the globalequilibrium equation of a laminate The generalized stressandmoment resultants in (18a) (18b) (18c) (19a) (19b) (19c)and (20) are defined as
(119872119896
119910
119872119896
119909119910
119873119896
119911
) = int
ℎ2
minusℎ2
(120590119910120601119896 120590119909119910120601119896 1205901199111206011015840
) d119911 (21a)
(119876119896
119909
119876119896
119910
119877119896
119910
) = int
ℎ2
minusℎ2
(1205901199091199111206011015840
119896
1205901199101199111206011015840
119896
120590119910119911120601119896) d119911 (21b)
(119872119909 119873119909119872119909119910 119876119909) = int
ℎ2
minusℎ2
(120590119909119911 120590119909 120590119909119910119911 120590119909119911) d119911 (21c)
Substitution (16) into (17) and subsequently into (21a) (21b)and (21c) generates the following relations
(119872119896
119910
119872119896
119909119910
119873119896
119911
)
= 120575119878(119863119896119895
26
119863119896119895
66
119861119896119895
36
)1198801015840
119895
+ (119863119896119895
22
119863119896119895
26
119861119895119896
23
)1198811015840
119895
+ (119861119896119895
23
119861119896119895
36
119860119896119895
33
)119882119895minus 120575119860(119863119896
26
119863119896
66
119861119896
36
) 1198611
+ 120575119862(119863119896
12
119863119896
16
119861119896
13
) 1198616+ (119861119896
12
119861119896
16
119860119896
13
) 1198612
(22a)
(119876119896
119909
119876119896
119910
119877119896
119910
)
= 120575119878(119860119896119895
55
119860119896119895
45
119861119896119895
45
)119880119895+ (119860119896119895
45
119860119896119895
44
119861119896119895
44
)119881119895
+ (119861119895119896
45
119861119895119896
44
119863119896119895
44
)1198821015840
119895
minus 120575119860(119860119896
55
119860119896
45
119861119896
45
) 1198611119910
(22b)
(119872119910119872119909119910 119873119909)
= 120575119878(119863119896
16
119863119896
66
119861119896
16
)1198801015840
119895
+ (119863119896
12
119863119896
26
119861119896
12
)1198811015840
119895
+ (119861119896
13
119861119896
36
119860119896
13
)119882119895minus 120575119860(11986316 11986366 11986116) 1198611
+ 120575119862(11986111 11986116 11986011) 1198616+ (11986311 11986316 11986111) 1198612
(22c)
119876119909= 120575119878119860119896
55
119880119895+ 119860119896
45
119881119895+ 119861119896
45
1198821015840
119895
+ 120575119860119860551198611119910 (22d)
The explicit expressions for the laminate rigidities appearingin (22a) (22b) (22c) and (22d) in terms of 119862
119894rsquos are presented
in the Appendix Direct substitution of (22a) (22b) (22c)and (22d) into (18a) (18b) and (18c) provides the localdisplacement equilibrium equations within LWTThe resultsare expressed as
120575119880119896 120575119878(119863119896119895
66
11988010158401015840
119895
minus 119860119896119895
55
119880119895+ 119863119896119895
26
11988110158401015840
119895
minus 119860119896119895
45
119881119895+ (119861119896119895
36
minus 119861119895119896
45
)1198821015840
119895
) = 120575119860119860119896
55
1198611119910
119896 = 1 2 119873 + 1
(23a)
120575119881119896 120575119878119863119896119895
26
11988010158401015840
119895
minus 120575119878119860119896119895
45
119880119895+ 119863119896119895
22
11988110158401015840
119895
minus 119860119896119895
44
119881119895+ (119861119896119895
23
minus 119861119895119896
44
)1198821015840
119895
= 120575119860119860119896
45
1198611119910
119896 = 1 2 119873 + 1
(23b)
120575119882119896 120575119878(119861119896119895
45
minus 119861119895119896
36
)1198801015840
119895
minus (119861119896119895
44
minus 119861119895119896
23
)1198811015840
119895
+ 119863119896119895
44
11988210158401015840
119895
minus 119860119896119895
33
119882119895
= minus120575119860(119861119896
45
+ 119861119896
36
) 1198611+ 119860119896
13
1198612+ 120575119862119861119896
13
1198616
119896 = 1 2 119873 + 1
(23c)
In the same way upon substitution of (16) into (17) andthe subsequent results into (19a) (19b) and (19c) the globalequations (19a) (19b) and (19c) are found in terms ofdisplacement functions as follows
1205751198611 120575119860int
119887
minus119887
((120575119878119860119896
55
119880119895+ 119860119896
45
119881119895+ 119861119896
45
1198821015840
119895
) 119910
minus (120575119878119863119896
66
1198801015840
119895
+ 119863119896
26
1198811015840
119895
+ 119861119896
36
119882119895)
+ 120575119860(1198605511986111199102
+ 11986366) 1198611minus 119861161198612
minus120575119862119863161198616) d119910 = 0
(24a)
6 International Journal of Engineering Mathematics
1205751198612 int119887
minus119887
(120575119878119861119896
16
1198801015840
119895
+ 119861119896
12
1198811015840
119895
+ 119860119896
13
119882119895
minus 120575119860119861161198611+ 119860111198612+ 120575119862119861111198616) d119910 = 0
(24b)
1205751198616 120575119862int
119887
minus119887
(120575119878119863119896
16
1198801015840
119895
+ 119863119896
12
1198811015840
119895
+ 119861119896
13
119882119895
minus 120575119860119863161198611+ 119861111198612+ 120575119862119863111198616) d119910 = 119872
0
(24c)
where the extra laminate rigidities appearing in (24a) (24b)and (24c) are defined in the Appendix The system ofequations in (23a) (23b) and (23c) shows 3(119873 + 1) coupledordinary differential equations with constant coefficientswhich may be indicated in a matrix form as
[119872] 12057810158401015840
+ [119870] 120578 = [119871] 119861 sdot 119910 (25)
where
120578 = 119880119879
119881119879
119882119879
119879
119880 = 1198801 1198802 119880
119873+1119879
119881 = 1198811 1198812 119881
119873+1119879
119882 = 11988211198822 119882
119873+1119879
(26)
119861 = 1198611 1198612 1198616119879
119882119895= int
119910
119882119895d119910
(27)
The coefficient matrices [119872] [119870] and [119871] in (25) are dis-played in the Appendix Also from the conditions in (3) andthe displacement field in (23a) (23b) and (23c) it is observedthat the functions 119880
119895 119881119895 and119882
119895are all odd functions of the
independent variable 119910 It can be confirmed that the generalsolution of (25) may be presented as
120578 = [120595] [sinh (120582119910)] 119867 + [119870]minus1
[119871] 119861 sdot 119910 (28)
where [sinh(120582119910)] is a 3(119873 + 1) times 3(119873 + 1) diagonal matrixand
[sinh (120582119910)]
= diag (sinh (1205821119910) sinh (120582
2119910) sinh (120582
3(119873+1)119910))
(29)
Also [120595] and (1205822
1
1205822
2
1205822
3(119873+1)
) are the model matrixand eigenvalues of (minus[119872]
minus1
[119870]) respectively 119870 is anunknown vector representing 3(119873+1) integration constantsThe constants 119861
119895(119895 = 1 2 6)must be calculated within LWT
analysis So the boundary conditions in (20) are first imposedto found the vector 119870 in terms of the unknown parameters119861119895(119895 = 1 2 6) These constants are next calculated in terms
of the specific bending moment 1198720by satisfaction of the
global equilibrium conditions in (19a) (19b) and (19c)
0 01 02 03 04 05 06 07 08 09 1
0
10
20
30
minus40
minus30
minus20
minus10
120590
120590z120590xz
Goodsell and Pipes (2013)Goodsell and Pipes (2013)
yb
mdashPresent solutionmdashPresent solution
Figure 2 Interlaminar stresses along the 45∘
minus45∘ interface of
[45∘
minus45∘
]119904
laminate
Table 1 Engineering properties of unidirectional graphiteopoxy[28]
1198641
(GPa)1198642
= 1198643
(GPa)11986612
= 11986613
(GPa)11986623
(GPa) 12059212
= 12059213
12059223
132 108 565 338 024 059
4 Numerical Results and Discussions
In this part several numerical examples are shown for thedistribution of interlaminar stress All physical layers areassumed to be of equal thickness (=05mm)Themechanicalproperties of unidirectional graphiteepoxy T3005208 usedin this study are shown in Table 1 [28]
Also each physical ply is modeled as being made up of 12numerical layers within LWT (ie 119901 = 12) In addition thewidth thickness ratio (ie 2119887ℎ) is assumed to be equal to 10Furthermore the stress components are normalized as
120590119894119895=120590119894119895
1205900
(30)
where 1205900= 1198720119887ℎ2
Figure 2 shows the distribution of interlaminar normaland shear stresses along the width of [45∘minus45∘]
119904laminate
Good correspondence was found between the present resultsand the results obtained by Goodsell and Pipes [29] whichconfirms the accuracy of the present solution Figure 3 showsthe distribution of interlaminar stresses 120590
119911and 120590
119910119911along the
minus45∘
0∘ and 120590
119909119911along the 0
∘
90∘ interfaces of the general
[45∘
minus 45∘
0∘
90∘
30∘
minus 30∘
] laminate It is seen that theinterlaminar stresses show high stress gradient near the freeedge It is observed that the interlaminar stresses 120590
119911and 120590
119909119911
grow quickly near the free edge while being zero in the innerregion of the laminate Also the magnitude of the transverseshear stress 120590
119909119911is greater than that of transverse normal stress
120590119911 On the other hand 120590
119910119911rises toward the free edge and
decreases suddenly to zero at free edgeThe interlaminar normal stress 120590
119911along the 90∘0∘ inter-
face of the unsymmetric cross-ply [90∘
0∘
90∘
0∘
90∘
0∘
]
International Journal of Engineering Mathematics 7
0
0
01 02
02
03 04
04
05 06
06
07 08 09 1
minus02
minus04
minus06
minus08
120590
120590xz at z = 0
120590z at z = h6120590yz at z = h6
yb
Figure 3 Distribution of interlaminar stresses 120590119911
and 120590119910119911
alongthe minus45∘0∘ and 120590
119909119911
along the 0∘90∘ interfaces of the [45∘ minus 45∘0∘
90∘
30∘
minus30∘
] laminate
0 02 04 06 08 1yb
minus4
0
minus8
minus12
minus16
120590z
2bh = 502bh = 20
2bh = 102bh = 5
Figure 4 Distribution of the interlaminar normal stress 120590119911
alongthe 90∘0∘ interface of the laminate for various width-to-thicknessratios
laminate for various width-to-thickness ratios is demon-strated in Figure 4 It is observed that by decreasingthe width-to-thickness ratio the boundary-layer region canbe expanded towards the internal region of the laminate withits width being almost equal to the thickness of the laminateIt is seen that the magnitude of the interlaminar stress at thefree edge is not varied as the width-to-thickness ratio of thelaminate is changed In addition the highly localized natureof interlaminar stresses near and exactly at the free edges ofthe laminate is apparent
The distribution of interlaminar stresses along the0∘
90∘ and 90
∘
0∘ interfaces of the unsymmetric cross-ply
[0∘90∘0∘90∘] and [90∘0∘90∘0∘] laminates respectivelyare compared in Figure 5 It is seen that the maximuminterfacial value 120590
119911at the 0
∘
90∘ and 90
∘
0∘ interfaces take
place at the free edge Figure 6 shows the variation ofinterlaminar normal stress 120590
119911on through-the-thickness and
near the free edge of the angle-ply [45∘minus 45∘45∘minus 45∘]laminate as the free edge is approached It is observed that
120590z at z =h4120590z at z
120590yz
120590yz at z120590yz at z = h4
minus14minus12minus1
minus08minus06minus04minus02
0020406
0 02 04 06 08 1
= h4= h4
in [0∘90∘0∘90∘]
in [0∘90∘0∘90∘]
in [90∘0∘90∘0∘]in [90∘0∘90∘0∘]
yb
Figure 5 Distribution of interlaminar stresses along the 0∘
90∘
and 90∘
0∘ interfaces of the [0∘90∘0∘90∘] and [90∘0∘90∘0∘]
laminates respectively
minus1
minus05
0
05
1
minus200 minus150 minus100 minus50 0 50 100 150 200
zh
y = 094by = 096b
y = 099by = b
120590z
Figure 6 Variations of interlaminar normal stress 120590119911
through thethickness of the [45∘minus45∘45∘minus45∘] laminate for various width-to-thickness ratios
the maximum negative and positive values of 120590119911occur within
the top minus80∘ layer and the bottom 80
∘ layer at the free edge(ie 119910 = 119887) respectively It is also noticed that 120590
119911diminishes
away from the free edge as the interior region of the laminateis approached Moreover 120590
119911reduces by moving slightly away
from the free edge and its distribution becomes smootherThe variations of the interlaminar shear stress 120590
119910119911at 119910 =
119887 through the thickness of the [0∘
60∘
minus60∘
]119904laminate are
displayed in Figure 7 By increasing the number of numericallayers in each lamina 120590
119910119911becomes slightly closer to zero but
8 International Journal of Engineering Mathematics
minus15
minus1
minus05
0
05
1
15
minus20 minus10 0 10 20 30
zh
p = 20
p = 12
p = 8
120590yz
Figure 7 Variations of interlaminar shear stress 120590119910119911
on through-thickness of the [0∘60∘minus60∘]119904
laminate as a function of layer subdivisionnumber 119901
012
01
008
006
004
002
0
minus002
120590z
p = 30p = 20
p = 12p = 8
0 02 04 06 08 1
yb
Figure 8 Variations of interlaminar normal stress 120590119911
on through-thickness of the [minus15∘
90∘
90∘
minus15∘
] laminate as a function of layersubdivision number 119901
it never becomes zero It should be noted that increasing thenumber of subdivisions results in no convergence for 120590
119911and
120590119909119911
at interface-edge junction of two dissimilar layers Thenumerical values of these components (120590
119911and 120590
119909119911) continue
to grow as the number of sublayers increased Since thegeneralized stress resultants 119877119896
119910
instead of 120590119910119911
are forced todisappear at the free edge in LWT the numerical value of120590119910119911
may never become zero at the interface-edge intersection
(even by increasing the number of sublayers in each physicallayer)
The distribution of interlaminar normal stress 120590119911on
through thickness of the general [minus15∘90∘90∘minus15∘] lam-inate is displayed in Figure 8 It is noted that increasingthe number of numerical layers (119901) in each lamina has nosignificant effect on the values of the interlaminar stress 120590
119911
within the boundary-layer region of the laminate expect
International Journal of Engineering Mathematics 9
exactly at the free edge (ie 119910 = 119887) Furthermore theinterlaminar normal stress 120590
119911grows rapidly in the vicinity of
the free edge while being zero in the interior region of thelaminate
5 Conclusions
In the present paper analytical solutions are developed toanalyze the interlaminar stresses for different lay-up con-figurations in laminated composite plates subjected to thebending moment The solutions were obtained based onthe reduced elasticity displacement field for long laminatedplates It is found that the components of the displacementsfield are composed of two distinct parts signifying theglobal and local deformations within laminates The localdisplacement functions as well as the interlaminar stressesthrough the layers of the laminate were found by Reddyrsquoslayerwise theory (LWT)Thenumerical results based onLWTwere shown for the free-edge interlaminar stresses throughthe thickness and across the interfaces of various cross-plysymmetric angle-ply and general composite laminates
Appendix
The laminate rigidities in (22a) (22b) (22c) (22d) (24a)(24b) and (24c) are defined as
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
1206011015840
119895
1206011198961206011015840
119895
120601119896120601119895) d119911
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
120601119896 1206011015840
119896
119911 120601119896119911) d119911
(119896 119895 = 1 2 119873 + 1)
(119860119901119902 119861119901119902 119863119901119902) =
119873
sum
119894=1
int
119911119894+1
119911119894
119862(119894)
119901119902
(1 119911 1199112
) d119911
(A1)
which upon integration are presented in the following form
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
)
=
(minus
119862(119896minus1)
119901119902
ℎ119896minus1
minus
119862(119896minus1)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
6) if 119895 = 119896 minus 1
(
119862(119896minus1)
119901119902
ℎ119896minus1
+
119862(119896)
119901119902
ℎ119896
119862(119896minus1)
119901119902
2minus
119862(119896)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
3+
ℎ119896119862(119896)
119901119902
3) if 119895 = 119896
(minus
119862(119896)
119901119902
ℎ119896
119862(119896)
119901119902
2
ℎ119896119862(119896)
119901119902
6) if 119895 = 119896 + 1
(0 0 0) if 119895 lt 119896 minus 1 or 119895 gt 119896 + 1
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
)
=
(minus119862(1)
119901119902
ℎ1119862(1)
119901119902
2 119862(1)
119901119902
1199112
1
minus 1199112
2
2ℎ1
119862(1)
119901119902
ℎ1
[1199113
1
minus 1199113
2
3minus 1199112
1199112
1
minus 1199112
2
2]) if 119896 = 1
(minus119862(119896minus1)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2]) if 119896 = 119873 + 1
(119862(119896minus1)
119901119902
minus 119862(119896)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2+
ℎ119896119862(119896)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
+ 119862(119896)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2] +
119862(119896)
119901119902
ℎ119896
[1199113
119896
minus 1199113
119896+1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896+1
2]) if 1 lt 119896 lt 119873 + 1
(A2)
10 International Journal of Engineering Mathematics
Also
(119860119901119902 119861119901119902 119863119901119902)
=
119873
sum
119894=1
119862(119894)
119901119902
([119911119894+1
minus 119911119894] [
1199112
119894+1
minus 1199112
119894
2] [
1199113
119894+1
minus 1199113
119894
3])
(A3)
The coefficient matrices [119872] [119870] and [119871] appearing in(25) are given as
[119872] =[[
[
120575119878[11986366] 120575119878[11986326] 120575119878([11986136] minus [119861
45]119879
)
120575119878[11986326] [119863
22] [119861
23] minus [119861
44]119879
[0] [0] [11986344]
]]
]
[119870]=[
[
minus120575119878([11986055] + [120572]) minus120575
119878[11986045] [0]
minus120575119878[11986045] minus ([119860
44] + [120572]) [0]
120575119878([11986145]minus[11986136]119879
) [11986144]minus[11986123]119879
minus ([11986033]+[120572])
]
]
[119871] = [
[
12057511986011986055 0 0
12057511986011986045 0 0
minus120575119860(11986145 + 119861
36) 119860
13 12057511986211986113
]
]
(A4)
where [119860119901119902] [119861119901119902] and [119863
119901119902] are (119873 + 1) times (119873 + 1) square
matrices containing 119860119896119895119901119902 119861119896119895119901119902 and 119863
119896119895
119901119902 respectively and the
vectors 119860119901119902 119861119901119902 and 119861
119901119902 are (119873+1)times1 columnmatrices
containing 119860119896119901119902
119861119896119901119902
and 119861119896
119901119902
respectively Also [0] is (119873 +
1) times (119873 + 1) square zero and 0 is a zero vector with 119873 + 1
rows The artificial matrix [120572] is also an (119873 + 1) times (119873 + 1)
square matrix whose elements are given by
120572119896119895
= 120572int
ℎ2
minusℎ2
120601119896120601119895d119911 (A5)
with 120572 being a relatively small parameter in comparison withthe rigidity constants 119860119896119895
119901119902(119901119902 = 33 44 55) It is noted that
the insertion of [120572] in the matrix [119870] makes the eigenvaluesof the matrix (minus[119872]
minus1
[119870]) distinct
References
[1] T Kant and K Swaminathan ldquoEstimation of transverseinter-laminar stresses in laminated compositesmdasha selective reviewand survey of current developmentsrdquo Composite Structures vol49 no 1 pp 65ndash75 2000
[2] A H Puppo and H A Evensen ldquoInterlaminar shear ınlamınated composıtes under generalızed plane stressrdquo Journalof Composite Materials vol 4 pp 204ndash220 1970
[3] N J Pagano ldquoOn the calculatıon of ınterlamınar normal stressın composıte lamınaterdquo Journal of Composite Materials vol 8pp 65ndash81 1974
[4] P W Hsu and C T Herakovich ldquoEdge effects in angle-plycomposite laminatesrdquo Journal of CompositeMaterials vol 11 pp422ndash428 1977
[5] S Tang and A Levy ldquoBoundary layer theory 2 extension oflaminated finite striprdquo Journal of CompositeMaterials vol 9 no1 pp 42ndash52 1975
[6] R B Pipes andN J Pagano ldquoInterlaminar stresses in compositelaminates an approximate elasticity solutionrdquo Journal of AppliedMechanics vol 41 no 3 pp 668ndash672 1974
[7] N J Pagano ldquoStress fields in composite laminatesrdquo InternationalJournal of Solids and Structures vol 14 no 5 pp 385ndash400 1978
[8] S S Wang and I Choi ldquoBoundary-layer effects in composıtelaminates 1 free-edge stress singulaiıtiesrdquo Journal of AppliedMechanics vol V 49 no 3 pp 541ndash548 1982
[9] W L Yin ldquoFree-edge effects in anisotropic laminates underextension bending and twisting part I a stress-function-basedvariational approachrdquo Journal of Applied Mechanics vol 61 no2 pp 410ndash415 1994
[10] A S D Wang and F W Crossman ldquoSome new results on edgeeffect in symmetric composite laminatesrdquo Journal of CompositeMaterials vol 11 no 1 pp 92ndash106 1977
[11] J D Whitcomb I S Raju and J G Goree ldquoReliability ofthe finite element method for calculating free edge stresses incomposite laminatesrdquo Computers and Structures vol 15 no 1pp 23ndash37 1982
[12] G Davı ldquoStress fields in general composite laminatesrdquo AIAAJournal vol 34 no 12 pp 2604ndash2608 1996
[13] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT Part 1 derivationof finite element matricesrdquo International Journal for NumericalMethods in Engineering vol 55 no 2 pp 191ndash231 2002
[14] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT part 2 numericalimplementationsrdquo International Journal for Numerical Methodsin Engineering vol 55 no 3 pp 253ndash291 2002
[15] V-T Nguyen and J-F Caron ldquoFinite element analysis of free-edge stresses in composite laminates under mechanical anthermal loadingrdquo Composites Science and Technology vol 69no 1 pp 40ndash49 2009
[16] D H Robbins Jr and J N Reddy ldquoModelling of thick compos-ites using a layerwise laminate theoryrdquo International Journal forNumerical Methods in Engineering vol 36 no 4 pp 655ndash6771993
[17] C Mittelstedt and W Becker ldquoReddyrsquos layerwise laminate platetheory for the computation of elastic fields in the vicinity ofstraight free laminate edgesrdquoMaterials Science and EngineeringA vol 498 no 1-2 pp 76ndash80 2008
[18] W J Na Damage analysis of laminated composite beams underbending loads using the layer-wise theory [Dissertation thesis]Texas AampM University Texas Tex USA 2008
[19] T S Plagianakos and D A Saravanos ldquoHigher-order layerwiselaminate theory for the prediction of interlaminar shear stressesin thick composite and sandwich composite platesrdquo CompositeStructures vol 87 no 1 pp 23ndash35 2009
[20] H Ullah A R Harland T Lucas D Price and V V Sil-berschmidt ldquoFinite-element modelling of bending of CFRPlaminates multiple delaminationsrdquo Computational MaterialsScience vol 52 no 1 pp 147ndash156 2012
[21] F Helenon M R Wisnom S R Hallett and R S TraskldquoInvestigation into failure of laminated composite T-piecespecimens under bending loadingrdquo Composites A vol 54 pp182ndash189 2013
[22] C H Thai A J M Ferreira E Carrera and H Nguyen-XuanldquoIsogeometric analysis of laminated composite and sandwichplates using a layerwise deformation theoryrdquo Composite Struc-tures vol 104 pp 196ndash214 2013
International Journal of Engineering Mathematics 11
[23] N D Thai M DrsquoOttavio and J-F Caron ldquoBending analysis oflaminated and sandwich plates using a layer-wise stress modelrdquoComposite Structures vol 96 pp 135ndash142 2013
[24] PMalekzadeh ldquoA two-dimensional layerwise-differential quad-rature static analysis of thick laminated composite circulararchesrdquoAppliedMathematicalModelling vol 33 no 4 pp 1850ndash1861 2009
[25] Y C Fung and P Tong Classical and Computational SolidMechanics World Scientific New Jersey NJ USA 2001
[26] S G LekhnitskiiTheory of Elasticity of anAnisotropic BodyMirPublishers Moscow Russia 1981
[27] A Nosier R K Kapania and J N Reddy ldquoFree vibrationanalysis of laminated plates using a layerwise theoryrdquo AIAAJournal vol 31 no 12 pp 2335ndash2346 1993
[28] C T HerakovichMechanics of Fibrous Composites Wiley NewYork NY USA 1998
[29] O Goodsell and R B Pipes ldquoInterlaminar stresses in compositelaminates subjected to anticlastic bending deformationrdquo Journalof Applied Mechanics vol 80 no 4 pp 1ndash7 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
4 International Journal of Engineering Mathematics
The displacement fields in (7) (9) and (11) can be repre-sented in one place as
119906(119896)
1
(119909 119910 119911) = 1198612119909 + 1205751198621198616119909119911 + 120575
119878119906(119896)
(119910 119911)
119906(119896)
2
(119909 119910 119911) = minus1205751198601198611119909119911 + V
(119896)
(119910 119911)
119906(119896)
3
(119909 119910 119911) = 1205751198601198611119909119910 minus
1
212057511986211986161199092
+ 119908(119896)
(119910 119911)
(12)
where 120575119860= 120575119878= 0 and 120575
119862= 1 for general cross-ply laminates
120575119860= 120575119862= 0 and 120575
119878= 1 for symmetric laminates 120575
119860= 120575119878= 1
and 120575119862= 0 for angle-ply laminates and 120575
119860= 120575119878= 120575119888= 1 for
general laminates
3 Layerwise Laminated Plate Theory of Reddy
In this section LWT is used for calculation of interlaminarstresses in arbitrary laminated composite plates with freeedges In LWT it is possible to replace the actual physicallayers to many mathematical layers [27] This can be doneby subdividing each physical layer through the thicknessto get the proper accuracy The theory assumes that thedisplacement components of a generic point in the laminateare given by [27]
1199061(119909 119910 119911) = 119906
119896(119909 119910) 120601
119896(119911)
1199062(119909 119910 119911) = V
119896(119909 119910) 120601
119896(119911)
1199063(119909 119910 119911) = 119908
119896(119909 119910) 120601
119896(119911)
119896 = 1 2 119873 + 1
(13)
It should be emphasized that a repeated index indicates sum-mation from 1 to119873 + 1 The functions 119906
119896(119909 119910) V
119896(119909 119910) and
119908119896(119909 119910) represent the displacements of the points initially
located at the kth plane of the laminate in the 119909 119910 and 119911
directions respectively The variable 119873 in (13) is the totalnumber of numerical layers introduced in any laminate Alsothe functions 120601
119896rsquos are the global approximation functions of
the thickness coordinate which are assumed here to be linear[27] This function expressed as
120601119896(119911) =
0 119911 le 119911119896minus1
1205952
119896minus1
(119911) 119911119896minus1
le 119911 le 119911119896
1205951
119896
(119911) 119911119896le 119911 le 119911
119896+1
0 119911 ge 119911119896+1
(119896 = 1 2 119873 + 1)
(14a)
where the local Lagrangian interpolation functions120595119895119896
(119911) (119895 =
1 2) related with the kth surface in the laminate are definedas
1205951
119896
(119911) =1
ℎ119896
(119911119896+1
minus 119911) 1205952
119896
(119911) =1
ℎ119896
(119911 minus 119911119896)
(14b)
where ℎ119896is the thickness of the kthmathematical layer Based
on the displacement field in (12) the displacement field ofLWT in (13) takes the following form
1199061(119909 119910 119911) = 120575
1198621198616119909119911 + 119861
2119909 + 120575119878119880119896(119910) 120601119896(119911)
1199062(119909 119910 119911) = minus120575
1198601198611119909119911 + 119881
119896(119910) 120601119896(119911)
1199063(119909 119910 119911) = 120575
1198601198611119909119910 minus
1
212057511986211986161199092
+119882119896(119910) 120601119896(119911)
119896 = 1 2 119873 + 1
(15)
It is noted that by the means of through-the-thicknesslinear interpolation functions the continuity of displacementcomponents through the thickness of laminate is identicallysatisfied On the other hand the transverse strain com-ponents remain discontinuous at the interfaces They willultimately emphasize the feasibility of having continuousinterlaminar stresses at the interfaces of adjoining layersby increasing the number of numerical layers through thephysical laminate Substituting (15) into the linear strain-displacement relations of elasticity [25] yields
120576119909= 1205751198621198616119911 + 1198612 120576
119910= 1198811015840
119896
120601119896 120576
119911= 1198821198961206011015840
119896
120574119910119911
= 1198811198961206011015840
119896
+1198821015840
119896
120601119896
120574119909119911
= 1205751198781198801198961206011015840
119896
+ 1205751198601198611119910 120574
119909119910= 1205751198781198801015840
119896
120601119896minus 1205751198601198611119911
(16)
where a prime in (16) denotes ordinary differentiation withrespect to a suitable independent variable (ie either 119910 or 119911)The three-dimensional constitutive law within the kth layer(with arbitrary fiber orientation) of the laminate may also beshown as [28]
(
(
120590119909
120590119910
120590119911
120590119910119911
120590119909119911
120590119909119910
)
)
(119896)
=
[[[[[[[[[
[
1198621111986212
11986213
0 0 11986216
11986212
11986222
11986223
0 0 11986226
11986213
11986223
11986233
0 0 11986236
0 0 0 11986244
11986245
0
0 0 0 11986245
11986255
0
11986216
11986226
11986236
0 0 11986266
]]]]]]]]]
]
(119896)
times(
(
120576119909
120576119910
120576119911
120574119910119911
120574119909119911
120574119909119910
)
)
(119896)
(17)
where [119862](119896) is the transformed (ie off axis) stiffness matrixof the kth layer By using the strain-displacement relations
International Journal of Engineering Mathematics 5
(16) in the principle of the minimum total potential energy[25] the equilibrium equations within LWT are found as
120575119880119896 120575119878(119876119896
119909
minus
d119872119896119909119910
d119910) = 0 119896 = 1 2 119873 + 1 (18a)
120575119881119896 119876119896119910
minus
d119872119896119910
d119910= 0 119896 = 1 2 119873 + 1 (18b)
120575119882119896 119873119896119911
minus
d119877119896119910
d119910= 0 119896 = 1 2 119873 + 1 (18c)
1205751198611 120575119860int
119887
minus119887
(119876119909119910 minus119872
119909119910) d119910 = 0 (19a)
1205751198612 int119887
minus119887
119873119909d119910 = 0 (19b)
1205751198616 120575119862int
119887
minus119887
119872119909d119910 = 119872
0 (19c)
Also the traction-free boundary conditions at the free edgesof the laminate are given as
119872119896
119910
= 119877119896
119910
= 120575119878119872119896
119909119910
= 0 at 119910 = plusmn119887 (119896 = 1 2 119873 + 1)
(20)
Equations (18a) (18b) and (18c) present 3(119873+1) local equilib-rium equations associated with119873+ 1 surface in the laminatewithin LWT Also (19a) (19b) and (19c) represent the globalequilibrium equation of a laminate The generalized stressandmoment resultants in (18a) (18b) (18c) (19a) (19b) (19c)and (20) are defined as
(119872119896
119910
119872119896
119909119910
119873119896
119911
) = int
ℎ2
minusℎ2
(120590119910120601119896 120590119909119910120601119896 1205901199111206011015840
) d119911 (21a)
(119876119896
119909
119876119896
119910
119877119896
119910
) = int
ℎ2
minusℎ2
(1205901199091199111206011015840
119896
1205901199101199111206011015840
119896
120590119910119911120601119896) d119911 (21b)
(119872119909 119873119909119872119909119910 119876119909) = int
ℎ2
minusℎ2
(120590119909119911 120590119909 120590119909119910119911 120590119909119911) d119911 (21c)
Substitution (16) into (17) and subsequently into (21a) (21b)and (21c) generates the following relations
(119872119896
119910
119872119896
119909119910
119873119896
119911
)
= 120575119878(119863119896119895
26
119863119896119895
66
119861119896119895
36
)1198801015840
119895
+ (119863119896119895
22
119863119896119895
26
119861119895119896
23
)1198811015840
119895
+ (119861119896119895
23
119861119896119895
36
119860119896119895
33
)119882119895minus 120575119860(119863119896
26
119863119896
66
119861119896
36
) 1198611
+ 120575119862(119863119896
12
119863119896
16
119861119896
13
) 1198616+ (119861119896
12
119861119896
16
119860119896
13
) 1198612
(22a)
(119876119896
119909
119876119896
119910
119877119896
119910
)
= 120575119878(119860119896119895
55
119860119896119895
45
119861119896119895
45
)119880119895+ (119860119896119895
45
119860119896119895
44
119861119896119895
44
)119881119895
+ (119861119895119896
45
119861119895119896
44
119863119896119895
44
)1198821015840
119895
minus 120575119860(119860119896
55
119860119896
45
119861119896
45
) 1198611119910
(22b)
(119872119910119872119909119910 119873119909)
= 120575119878(119863119896
16
119863119896
66
119861119896
16
)1198801015840
119895
+ (119863119896
12
119863119896
26
119861119896
12
)1198811015840
119895
+ (119861119896
13
119861119896
36
119860119896
13
)119882119895minus 120575119860(11986316 11986366 11986116) 1198611
+ 120575119862(11986111 11986116 11986011) 1198616+ (11986311 11986316 11986111) 1198612
(22c)
119876119909= 120575119878119860119896
55
119880119895+ 119860119896
45
119881119895+ 119861119896
45
1198821015840
119895
+ 120575119860119860551198611119910 (22d)
The explicit expressions for the laminate rigidities appearingin (22a) (22b) (22c) and (22d) in terms of 119862
119894rsquos are presented
in the Appendix Direct substitution of (22a) (22b) (22c)and (22d) into (18a) (18b) and (18c) provides the localdisplacement equilibrium equations within LWTThe resultsare expressed as
120575119880119896 120575119878(119863119896119895
66
11988010158401015840
119895
minus 119860119896119895
55
119880119895+ 119863119896119895
26
11988110158401015840
119895
minus 119860119896119895
45
119881119895+ (119861119896119895
36
minus 119861119895119896
45
)1198821015840
119895
) = 120575119860119860119896
55
1198611119910
119896 = 1 2 119873 + 1
(23a)
120575119881119896 120575119878119863119896119895
26
11988010158401015840
119895
minus 120575119878119860119896119895
45
119880119895+ 119863119896119895
22
11988110158401015840
119895
minus 119860119896119895
44
119881119895+ (119861119896119895
23
minus 119861119895119896
44
)1198821015840
119895
= 120575119860119860119896
45
1198611119910
119896 = 1 2 119873 + 1
(23b)
120575119882119896 120575119878(119861119896119895
45
minus 119861119895119896
36
)1198801015840
119895
minus (119861119896119895
44
minus 119861119895119896
23
)1198811015840
119895
+ 119863119896119895
44
11988210158401015840
119895
minus 119860119896119895
33
119882119895
= minus120575119860(119861119896
45
+ 119861119896
36
) 1198611+ 119860119896
13
1198612+ 120575119862119861119896
13
1198616
119896 = 1 2 119873 + 1
(23c)
In the same way upon substitution of (16) into (17) andthe subsequent results into (19a) (19b) and (19c) the globalequations (19a) (19b) and (19c) are found in terms ofdisplacement functions as follows
1205751198611 120575119860int
119887
minus119887
((120575119878119860119896
55
119880119895+ 119860119896
45
119881119895+ 119861119896
45
1198821015840
119895
) 119910
minus (120575119878119863119896
66
1198801015840
119895
+ 119863119896
26
1198811015840
119895
+ 119861119896
36
119882119895)
+ 120575119860(1198605511986111199102
+ 11986366) 1198611minus 119861161198612
minus120575119862119863161198616) d119910 = 0
(24a)
6 International Journal of Engineering Mathematics
1205751198612 int119887
minus119887
(120575119878119861119896
16
1198801015840
119895
+ 119861119896
12
1198811015840
119895
+ 119860119896
13
119882119895
minus 120575119860119861161198611+ 119860111198612+ 120575119862119861111198616) d119910 = 0
(24b)
1205751198616 120575119862int
119887
minus119887
(120575119878119863119896
16
1198801015840
119895
+ 119863119896
12
1198811015840
119895
+ 119861119896
13
119882119895
minus 120575119860119863161198611+ 119861111198612+ 120575119862119863111198616) d119910 = 119872
0
(24c)
where the extra laminate rigidities appearing in (24a) (24b)and (24c) are defined in the Appendix The system ofequations in (23a) (23b) and (23c) shows 3(119873 + 1) coupledordinary differential equations with constant coefficientswhich may be indicated in a matrix form as
[119872] 12057810158401015840
+ [119870] 120578 = [119871] 119861 sdot 119910 (25)
where
120578 = 119880119879
119881119879
119882119879
119879
119880 = 1198801 1198802 119880
119873+1119879
119881 = 1198811 1198812 119881
119873+1119879
119882 = 11988211198822 119882
119873+1119879
(26)
119861 = 1198611 1198612 1198616119879
119882119895= int
119910
119882119895d119910
(27)
The coefficient matrices [119872] [119870] and [119871] in (25) are dis-played in the Appendix Also from the conditions in (3) andthe displacement field in (23a) (23b) and (23c) it is observedthat the functions 119880
119895 119881119895 and119882
119895are all odd functions of the
independent variable 119910 It can be confirmed that the generalsolution of (25) may be presented as
120578 = [120595] [sinh (120582119910)] 119867 + [119870]minus1
[119871] 119861 sdot 119910 (28)
where [sinh(120582119910)] is a 3(119873 + 1) times 3(119873 + 1) diagonal matrixand
[sinh (120582119910)]
= diag (sinh (1205821119910) sinh (120582
2119910) sinh (120582
3(119873+1)119910))
(29)
Also [120595] and (1205822
1
1205822
2
1205822
3(119873+1)
) are the model matrixand eigenvalues of (minus[119872]
minus1
[119870]) respectively 119870 is anunknown vector representing 3(119873+1) integration constantsThe constants 119861
119895(119895 = 1 2 6)must be calculated within LWT
analysis So the boundary conditions in (20) are first imposedto found the vector 119870 in terms of the unknown parameters119861119895(119895 = 1 2 6) These constants are next calculated in terms
of the specific bending moment 1198720by satisfaction of the
global equilibrium conditions in (19a) (19b) and (19c)
0 01 02 03 04 05 06 07 08 09 1
0
10
20
30
minus40
minus30
minus20
minus10
120590
120590z120590xz
Goodsell and Pipes (2013)Goodsell and Pipes (2013)
yb
mdashPresent solutionmdashPresent solution
Figure 2 Interlaminar stresses along the 45∘
minus45∘ interface of
[45∘
minus45∘
]119904
laminate
Table 1 Engineering properties of unidirectional graphiteopoxy[28]
1198641
(GPa)1198642
= 1198643
(GPa)11986612
= 11986613
(GPa)11986623
(GPa) 12059212
= 12059213
12059223
132 108 565 338 024 059
4 Numerical Results and Discussions
In this part several numerical examples are shown for thedistribution of interlaminar stress All physical layers areassumed to be of equal thickness (=05mm)Themechanicalproperties of unidirectional graphiteepoxy T3005208 usedin this study are shown in Table 1 [28]
Also each physical ply is modeled as being made up of 12numerical layers within LWT (ie 119901 = 12) In addition thewidth thickness ratio (ie 2119887ℎ) is assumed to be equal to 10Furthermore the stress components are normalized as
120590119894119895=120590119894119895
1205900
(30)
where 1205900= 1198720119887ℎ2
Figure 2 shows the distribution of interlaminar normaland shear stresses along the width of [45∘minus45∘]
119904laminate
Good correspondence was found between the present resultsand the results obtained by Goodsell and Pipes [29] whichconfirms the accuracy of the present solution Figure 3 showsthe distribution of interlaminar stresses 120590
119911and 120590
119910119911along the
minus45∘
0∘ and 120590
119909119911along the 0
∘
90∘ interfaces of the general
[45∘
minus 45∘
0∘
90∘
30∘
minus 30∘
] laminate It is seen that theinterlaminar stresses show high stress gradient near the freeedge It is observed that the interlaminar stresses 120590
119911and 120590
119909119911
grow quickly near the free edge while being zero in the innerregion of the laminate Also the magnitude of the transverseshear stress 120590
119909119911is greater than that of transverse normal stress
120590119911 On the other hand 120590
119910119911rises toward the free edge and
decreases suddenly to zero at free edgeThe interlaminar normal stress 120590
119911along the 90∘0∘ inter-
face of the unsymmetric cross-ply [90∘
0∘
90∘
0∘
90∘
0∘
]
International Journal of Engineering Mathematics 7
0
0
01 02
02
03 04
04
05 06
06
07 08 09 1
minus02
minus04
minus06
minus08
120590
120590xz at z = 0
120590z at z = h6120590yz at z = h6
yb
Figure 3 Distribution of interlaminar stresses 120590119911
and 120590119910119911
alongthe minus45∘0∘ and 120590
119909119911
along the 0∘90∘ interfaces of the [45∘ minus 45∘0∘
90∘
30∘
minus30∘
] laminate
0 02 04 06 08 1yb
minus4
0
minus8
minus12
minus16
120590z
2bh = 502bh = 20
2bh = 102bh = 5
Figure 4 Distribution of the interlaminar normal stress 120590119911
alongthe 90∘0∘ interface of the laminate for various width-to-thicknessratios
laminate for various width-to-thickness ratios is demon-strated in Figure 4 It is observed that by decreasingthe width-to-thickness ratio the boundary-layer region canbe expanded towards the internal region of the laminate withits width being almost equal to the thickness of the laminateIt is seen that the magnitude of the interlaminar stress at thefree edge is not varied as the width-to-thickness ratio of thelaminate is changed In addition the highly localized natureof interlaminar stresses near and exactly at the free edges ofthe laminate is apparent
The distribution of interlaminar stresses along the0∘
90∘ and 90
∘
0∘ interfaces of the unsymmetric cross-ply
[0∘90∘0∘90∘] and [90∘0∘90∘0∘] laminates respectivelyare compared in Figure 5 It is seen that the maximuminterfacial value 120590
119911at the 0
∘
90∘ and 90
∘
0∘ interfaces take
place at the free edge Figure 6 shows the variation ofinterlaminar normal stress 120590
119911on through-the-thickness and
near the free edge of the angle-ply [45∘minus 45∘45∘minus 45∘]laminate as the free edge is approached It is observed that
120590z at z =h4120590z at z
120590yz
120590yz at z120590yz at z = h4
minus14minus12minus1
minus08minus06minus04minus02
0020406
0 02 04 06 08 1
= h4= h4
in [0∘90∘0∘90∘]
in [0∘90∘0∘90∘]
in [90∘0∘90∘0∘]in [90∘0∘90∘0∘]
yb
Figure 5 Distribution of interlaminar stresses along the 0∘
90∘
and 90∘
0∘ interfaces of the [0∘90∘0∘90∘] and [90∘0∘90∘0∘]
laminates respectively
minus1
minus05
0
05
1
minus200 minus150 minus100 minus50 0 50 100 150 200
zh
y = 094by = 096b
y = 099by = b
120590z
Figure 6 Variations of interlaminar normal stress 120590119911
through thethickness of the [45∘minus45∘45∘minus45∘] laminate for various width-to-thickness ratios
the maximum negative and positive values of 120590119911occur within
the top minus80∘ layer and the bottom 80
∘ layer at the free edge(ie 119910 = 119887) respectively It is also noticed that 120590
119911diminishes
away from the free edge as the interior region of the laminateis approached Moreover 120590
119911reduces by moving slightly away
from the free edge and its distribution becomes smootherThe variations of the interlaminar shear stress 120590
119910119911at 119910 =
119887 through the thickness of the [0∘
60∘
minus60∘
]119904laminate are
displayed in Figure 7 By increasing the number of numericallayers in each lamina 120590
119910119911becomes slightly closer to zero but
8 International Journal of Engineering Mathematics
minus15
minus1
minus05
0
05
1
15
minus20 minus10 0 10 20 30
zh
p = 20
p = 12
p = 8
120590yz
Figure 7 Variations of interlaminar shear stress 120590119910119911
on through-thickness of the [0∘60∘minus60∘]119904
laminate as a function of layer subdivisionnumber 119901
012
01
008
006
004
002
0
minus002
120590z
p = 30p = 20
p = 12p = 8
0 02 04 06 08 1
yb
Figure 8 Variations of interlaminar normal stress 120590119911
on through-thickness of the [minus15∘
90∘
90∘
minus15∘
] laminate as a function of layersubdivision number 119901
it never becomes zero It should be noted that increasing thenumber of subdivisions results in no convergence for 120590
119911and
120590119909119911
at interface-edge junction of two dissimilar layers Thenumerical values of these components (120590
119911and 120590
119909119911) continue
to grow as the number of sublayers increased Since thegeneralized stress resultants 119877119896
119910
instead of 120590119910119911
are forced todisappear at the free edge in LWT the numerical value of120590119910119911
may never become zero at the interface-edge intersection
(even by increasing the number of sublayers in each physicallayer)
The distribution of interlaminar normal stress 120590119911on
through thickness of the general [minus15∘90∘90∘minus15∘] lam-inate is displayed in Figure 8 It is noted that increasingthe number of numerical layers (119901) in each lamina has nosignificant effect on the values of the interlaminar stress 120590
119911
within the boundary-layer region of the laminate expect
International Journal of Engineering Mathematics 9
exactly at the free edge (ie 119910 = 119887) Furthermore theinterlaminar normal stress 120590
119911grows rapidly in the vicinity of
the free edge while being zero in the interior region of thelaminate
5 Conclusions
In the present paper analytical solutions are developed toanalyze the interlaminar stresses for different lay-up con-figurations in laminated composite plates subjected to thebending moment The solutions were obtained based onthe reduced elasticity displacement field for long laminatedplates It is found that the components of the displacementsfield are composed of two distinct parts signifying theglobal and local deformations within laminates The localdisplacement functions as well as the interlaminar stressesthrough the layers of the laminate were found by Reddyrsquoslayerwise theory (LWT)Thenumerical results based onLWTwere shown for the free-edge interlaminar stresses throughthe thickness and across the interfaces of various cross-plysymmetric angle-ply and general composite laminates
Appendix
The laminate rigidities in (22a) (22b) (22c) (22d) (24a)(24b) and (24c) are defined as
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
1206011015840
119895
1206011198961206011015840
119895
120601119896120601119895) d119911
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
120601119896 1206011015840
119896
119911 120601119896119911) d119911
(119896 119895 = 1 2 119873 + 1)
(119860119901119902 119861119901119902 119863119901119902) =
119873
sum
119894=1
int
119911119894+1
119911119894
119862(119894)
119901119902
(1 119911 1199112
) d119911
(A1)
which upon integration are presented in the following form
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
)
=
(minus
119862(119896minus1)
119901119902
ℎ119896minus1
minus
119862(119896minus1)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
6) if 119895 = 119896 minus 1
(
119862(119896minus1)
119901119902
ℎ119896minus1
+
119862(119896)
119901119902
ℎ119896
119862(119896minus1)
119901119902
2minus
119862(119896)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
3+
ℎ119896119862(119896)
119901119902
3) if 119895 = 119896
(minus
119862(119896)
119901119902
ℎ119896
119862(119896)
119901119902
2
ℎ119896119862(119896)
119901119902
6) if 119895 = 119896 + 1
(0 0 0) if 119895 lt 119896 minus 1 or 119895 gt 119896 + 1
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
)
=
(minus119862(1)
119901119902
ℎ1119862(1)
119901119902
2 119862(1)
119901119902
1199112
1
minus 1199112
2
2ℎ1
119862(1)
119901119902
ℎ1
[1199113
1
minus 1199113
2
3minus 1199112
1199112
1
minus 1199112
2
2]) if 119896 = 1
(minus119862(119896minus1)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2]) if 119896 = 119873 + 1
(119862(119896minus1)
119901119902
minus 119862(119896)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2+
ℎ119896119862(119896)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
+ 119862(119896)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2] +
119862(119896)
119901119902
ℎ119896
[1199113
119896
minus 1199113
119896+1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896+1
2]) if 1 lt 119896 lt 119873 + 1
(A2)
10 International Journal of Engineering Mathematics
Also
(119860119901119902 119861119901119902 119863119901119902)
=
119873
sum
119894=1
119862(119894)
119901119902
([119911119894+1
minus 119911119894] [
1199112
119894+1
minus 1199112
119894
2] [
1199113
119894+1
minus 1199113
119894
3])
(A3)
The coefficient matrices [119872] [119870] and [119871] appearing in(25) are given as
[119872] =[[
[
120575119878[11986366] 120575119878[11986326] 120575119878([11986136] minus [119861
45]119879
)
120575119878[11986326] [119863
22] [119861
23] minus [119861
44]119879
[0] [0] [11986344]
]]
]
[119870]=[
[
minus120575119878([11986055] + [120572]) minus120575
119878[11986045] [0]
minus120575119878[11986045] minus ([119860
44] + [120572]) [0]
120575119878([11986145]minus[11986136]119879
) [11986144]minus[11986123]119879
minus ([11986033]+[120572])
]
]
[119871] = [
[
12057511986011986055 0 0
12057511986011986045 0 0
minus120575119860(11986145 + 119861
36) 119860
13 12057511986211986113
]
]
(A4)
where [119860119901119902] [119861119901119902] and [119863
119901119902] are (119873 + 1) times (119873 + 1) square
matrices containing 119860119896119895119901119902 119861119896119895119901119902 and 119863
119896119895
119901119902 respectively and the
vectors 119860119901119902 119861119901119902 and 119861
119901119902 are (119873+1)times1 columnmatrices
containing 119860119896119901119902
119861119896119901119902
and 119861119896
119901119902
respectively Also [0] is (119873 +
1) times (119873 + 1) square zero and 0 is a zero vector with 119873 + 1
rows The artificial matrix [120572] is also an (119873 + 1) times (119873 + 1)
square matrix whose elements are given by
120572119896119895
= 120572int
ℎ2
minusℎ2
120601119896120601119895d119911 (A5)
with 120572 being a relatively small parameter in comparison withthe rigidity constants 119860119896119895
119901119902(119901119902 = 33 44 55) It is noted that
the insertion of [120572] in the matrix [119870] makes the eigenvaluesof the matrix (minus[119872]
minus1
[119870]) distinct
References
[1] T Kant and K Swaminathan ldquoEstimation of transverseinter-laminar stresses in laminated compositesmdasha selective reviewand survey of current developmentsrdquo Composite Structures vol49 no 1 pp 65ndash75 2000
[2] A H Puppo and H A Evensen ldquoInterlaminar shear ınlamınated composıtes under generalızed plane stressrdquo Journalof Composite Materials vol 4 pp 204ndash220 1970
[3] N J Pagano ldquoOn the calculatıon of ınterlamınar normal stressın composıte lamınaterdquo Journal of Composite Materials vol 8pp 65ndash81 1974
[4] P W Hsu and C T Herakovich ldquoEdge effects in angle-plycomposite laminatesrdquo Journal of CompositeMaterials vol 11 pp422ndash428 1977
[5] S Tang and A Levy ldquoBoundary layer theory 2 extension oflaminated finite striprdquo Journal of CompositeMaterials vol 9 no1 pp 42ndash52 1975
[6] R B Pipes andN J Pagano ldquoInterlaminar stresses in compositelaminates an approximate elasticity solutionrdquo Journal of AppliedMechanics vol 41 no 3 pp 668ndash672 1974
[7] N J Pagano ldquoStress fields in composite laminatesrdquo InternationalJournal of Solids and Structures vol 14 no 5 pp 385ndash400 1978
[8] S S Wang and I Choi ldquoBoundary-layer effects in composıtelaminates 1 free-edge stress singulaiıtiesrdquo Journal of AppliedMechanics vol V 49 no 3 pp 541ndash548 1982
[9] W L Yin ldquoFree-edge effects in anisotropic laminates underextension bending and twisting part I a stress-function-basedvariational approachrdquo Journal of Applied Mechanics vol 61 no2 pp 410ndash415 1994
[10] A S D Wang and F W Crossman ldquoSome new results on edgeeffect in symmetric composite laminatesrdquo Journal of CompositeMaterials vol 11 no 1 pp 92ndash106 1977
[11] J D Whitcomb I S Raju and J G Goree ldquoReliability ofthe finite element method for calculating free edge stresses incomposite laminatesrdquo Computers and Structures vol 15 no 1pp 23ndash37 1982
[12] G Davı ldquoStress fields in general composite laminatesrdquo AIAAJournal vol 34 no 12 pp 2604ndash2608 1996
[13] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT Part 1 derivationof finite element matricesrdquo International Journal for NumericalMethods in Engineering vol 55 no 2 pp 191ndash231 2002
[14] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT part 2 numericalimplementationsrdquo International Journal for Numerical Methodsin Engineering vol 55 no 3 pp 253ndash291 2002
[15] V-T Nguyen and J-F Caron ldquoFinite element analysis of free-edge stresses in composite laminates under mechanical anthermal loadingrdquo Composites Science and Technology vol 69no 1 pp 40ndash49 2009
[16] D H Robbins Jr and J N Reddy ldquoModelling of thick compos-ites using a layerwise laminate theoryrdquo International Journal forNumerical Methods in Engineering vol 36 no 4 pp 655ndash6771993
[17] C Mittelstedt and W Becker ldquoReddyrsquos layerwise laminate platetheory for the computation of elastic fields in the vicinity ofstraight free laminate edgesrdquoMaterials Science and EngineeringA vol 498 no 1-2 pp 76ndash80 2008
[18] W J Na Damage analysis of laminated composite beams underbending loads using the layer-wise theory [Dissertation thesis]Texas AampM University Texas Tex USA 2008
[19] T S Plagianakos and D A Saravanos ldquoHigher-order layerwiselaminate theory for the prediction of interlaminar shear stressesin thick composite and sandwich composite platesrdquo CompositeStructures vol 87 no 1 pp 23ndash35 2009
[20] H Ullah A R Harland T Lucas D Price and V V Sil-berschmidt ldquoFinite-element modelling of bending of CFRPlaminates multiple delaminationsrdquo Computational MaterialsScience vol 52 no 1 pp 147ndash156 2012
[21] F Helenon M R Wisnom S R Hallett and R S TraskldquoInvestigation into failure of laminated composite T-piecespecimens under bending loadingrdquo Composites A vol 54 pp182ndash189 2013
[22] C H Thai A J M Ferreira E Carrera and H Nguyen-XuanldquoIsogeometric analysis of laminated composite and sandwichplates using a layerwise deformation theoryrdquo Composite Struc-tures vol 104 pp 196ndash214 2013
International Journal of Engineering Mathematics 11
[23] N D Thai M DrsquoOttavio and J-F Caron ldquoBending analysis oflaminated and sandwich plates using a layer-wise stress modelrdquoComposite Structures vol 96 pp 135ndash142 2013
[24] PMalekzadeh ldquoA two-dimensional layerwise-differential quad-rature static analysis of thick laminated composite circulararchesrdquoAppliedMathematicalModelling vol 33 no 4 pp 1850ndash1861 2009
[25] Y C Fung and P Tong Classical and Computational SolidMechanics World Scientific New Jersey NJ USA 2001
[26] S G LekhnitskiiTheory of Elasticity of anAnisotropic BodyMirPublishers Moscow Russia 1981
[27] A Nosier R K Kapania and J N Reddy ldquoFree vibrationanalysis of laminated plates using a layerwise theoryrdquo AIAAJournal vol 31 no 12 pp 2335ndash2346 1993
[28] C T HerakovichMechanics of Fibrous Composites Wiley NewYork NY USA 1998
[29] O Goodsell and R B Pipes ldquoInterlaminar stresses in compositelaminates subjected to anticlastic bending deformationrdquo Journalof Applied Mechanics vol 80 no 4 pp 1ndash7 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
International Journal of Engineering Mathematics 5
(16) in the principle of the minimum total potential energy[25] the equilibrium equations within LWT are found as
120575119880119896 120575119878(119876119896
119909
minus
d119872119896119909119910
d119910) = 0 119896 = 1 2 119873 + 1 (18a)
120575119881119896 119876119896119910
minus
d119872119896119910
d119910= 0 119896 = 1 2 119873 + 1 (18b)
120575119882119896 119873119896119911
minus
d119877119896119910
d119910= 0 119896 = 1 2 119873 + 1 (18c)
1205751198611 120575119860int
119887
minus119887
(119876119909119910 minus119872
119909119910) d119910 = 0 (19a)
1205751198612 int119887
minus119887
119873119909d119910 = 0 (19b)
1205751198616 120575119862int
119887
minus119887
119872119909d119910 = 119872
0 (19c)
Also the traction-free boundary conditions at the free edgesof the laminate are given as
119872119896
119910
= 119877119896
119910
= 120575119878119872119896
119909119910
= 0 at 119910 = plusmn119887 (119896 = 1 2 119873 + 1)
(20)
Equations (18a) (18b) and (18c) present 3(119873+1) local equilib-rium equations associated with119873+ 1 surface in the laminatewithin LWT Also (19a) (19b) and (19c) represent the globalequilibrium equation of a laminate The generalized stressandmoment resultants in (18a) (18b) (18c) (19a) (19b) (19c)and (20) are defined as
(119872119896
119910
119872119896
119909119910
119873119896
119911
) = int
ℎ2
minusℎ2
(120590119910120601119896 120590119909119910120601119896 1205901199111206011015840
) d119911 (21a)
(119876119896
119909
119876119896
119910
119877119896
119910
) = int
ℎ2
minusℎ2
(1205901199091199111206011015840
119896
1205901199101199111206011015840
119896
120590119910119911120601119896) d119911 (21b)
(119872119909 119873119909119872119909119910 119876119909) = int
ℎ2
minusℎ2
(120590119909119911 120590119909 120590119909119910119911 120590119909119911) d119911 (21c)
Substitution (16) into (17) and subsequently into (21a) (21b)and (21c) generates the following relations
(119872119896
119910
119872119896
119909119910
119873119896
119911
)
= 120575119878(119863119896119895
26
119863119896119895
66
119861119896119895
36
)1198801015840
119895
+ (119863119896119895
22
119863119896119895
26
119861119895119896
23
)1198811015840
119895
+ (119861119896119895
23
119861119896119895
36
119860119896119895
33
)119882119895minus 120575119860(119863119896
26
119863119896
66
119861119896
36
) 1198611
+ 120575119862(119863119896
12
119863119896
16
119861119896
13
) 1198616+ (119861119896
12
119861119896
16
119860119896
13
) 1198612
(22a)
(119876119896
119909
119876119896
119910
119877119896
119910
)
= 120575119878(119860119896119895
55
119860119896119895
45
119861119896119895
45
)119880119895+ (119860119896119895
45
119860119896119895
44
119861119896119895
44
)119881119895
+ (119861119895119896
45
119861119895119896
44
119863119896119895
44
)1198821015840
119895
minus 120575119860(119860119896
55
119860119896
45
119861119896
45
) 1198611119910
(22b)
(119872119910119872119909119910 119873119909)
= 120575119878(119863119896
16
119863119896
66
119861119896
16
)1198801015840
119895
+ (119863119896
12
119863119896
26
119861119896
12
)1198811015840
119895
+ (119861119896
13
119861119896
36
119860119896
13
)119882119895minus 120575119860(11986316 11986366 11986116) 1198611
+ 120575119862(11986111 11986116 11986011) 1198616+ (11986311 11986316 11986111) 1198612
(22c)
119876119909= 120575119878119860119896
55
119880119895+ 119860119896
45
119881119895+ 119861119896
45
1198821015840
119895
+ 120575119860119860551198611119910 (22d)
The explicit expressions for the laminate rigidities appearingin (22a) (22b) (22c) and (22d) in terms of 119862
119894rsquos are presented
in the Appendix Direct substitution of (22a) (22b) (22c)and (22d) into (18a) (18b) and (18c) provides the localdisplacement equilibrium equations within LWTThe resultsare expressed as
120575119880119896 120575119878(119863119896119895
66
11988010158401015840
119895
minus 119860119896119895
55
119880119895+ 119863119896119895
26
11988110158401015840
119895
minus 119860119896119895
45
119881119895+ (119861119896119895
36
minus 119861119895119896
45
)1198821015840
119895
) = 120575119860119860119896
55
1198611119910
119896 = 1 2 119873 + 1
(23a)
120575119881119896 120575119878119863119896119895
26
11988010158401015840
119895
minus 120575119878119860119896119895
45
119880119895+ 119863119896119895
22
11988110158401015840
119895
minus 119860119896119895
44
119881119895+ (119861119896119895
23
minus 119861119895119896
44
)1198821015840
119895
= 120575119860119860119896
45
1198611119910
119896 = 1 2 119873 + 1
(23b)
120575119882119896 120575119878(119861119896119895
45
minus 119861119895119896
36
)1198801015840
119895
minus (119861119896119895
44
minus 119861119895119896
23
)1198811015840
119895
+ 119863119896119895
44
11988210158401015840
119895
minus 119860119896119895
33
119882119895
= minus120575119860(119861119896
45
+ 119861119896
36
) 1198611+ 119860119896
13
1198612+ 120575119862119861119896
13
1198616
119896 = 1 2 119873 + 1
(23c)
In the same way upon substitution of (16) into (17) andthe subsequent results into (19a) (19b) and (19c) the globalequations (19a) (19b) and (19c) are found in terms ofdisplacement functions as follows
1205751198611 120575119860int
119887
minus119887
((120575119878119860119896
55
119880119895+ 119860119896
45
119881119895+ 119861119896
45
1198821015840
119895
) 119910
minus (120575119878119863119896
66
1198801015840
119895
+ 119863119896
26
1198811015840
119895
+ 119861119896
36
119882119895)
+ 120575119860(1198605511986111199102
+ 11986366) 1198611minus 119861161198612
minus120575119862119863161198616) d119910 = 0
(24a)
6 International Journal of Engineering Mathematics
1205751198612 int119887
minus119887
(120575119878119861119896
16
1198801015840
119895
+ 119861119896
12
1198811015840
119895
+ 119860119896
13
119882119895
minus 120575119860119861161198611+ 119860111198612+ 120575119862119861111198616) d119910 = 0
(24b)
1205751198616 120575119862int
119887
minus119887
(120575119878119863119896
16
1198801015840
119895
+ 119863119896
12
1198811015840
119895
+ 119861119896
13
119882119895
minus 120575119860119863161198611+ 119861111198612+ 120575119862119863111198616) d119910 = 119872
0
(24c)
where the extra laminate rigidities appearing in (24a) (24b)and (24c) are defined in the Appendix The system ofequations in (23a) (23b) and (23c) shows 3(119873 + 1) coupledordinary differential equations with constant coefficientswhich may be indicated in a matrix form as
[119872] 12057810158401015840
+ [119870] 120578 = [119871] 119861 sdot 119910 (25)
where
120578 = 119880119879
119881119879
119882119879
119879
119880 = 1198801 1198802 119880
119873+1119879
119881 = 1198811 1198812 119881
119873+1119879
119882 = 11988211198822 119882
119873+1119879
(26)
119861 = 1198611 1198612 1198616119879
119882119895= int
119910
119882119895d119910
(27)
The coefficient matrices [119872] [119870] and [119871] in (25) are dis-played in the Appendix Also from the conditions in (3) andthe displacement field in (23a) (23b) and (23c) it is observedthat the functions 119880
119895 119881119895 and119882
119895are all odd functions of the
independent variable 119910 It can be confirmed that the generalsolution of (25) may be presented as
120578 = [120595] [sinh (120582119910)] 119867 + [119870]minus1
[119871] 119861 sdot 119910 (28)
where [sinh(120582119910)] is a 3(119873 + 1) times 3(119873 + 1) diagonal matrixand
[sinh (120582119910)]
= diag (sinh (1205821119910) sinh (120582
2119910) sinh (120582
3(119873+1)119910))
(29)
Also [120595] and (1205822
1
1205822
2
1205822
3(119873+1)
) are the model matrixand eigenvalues of (minus[119872]
minus1
[119870]) respectively 119870 is anunknown vector representing 3(119873+1) integration constantsThe constants 119861
119895(119895 = 1 2 6)must be calculated within LWT
analysis So the boundary conditions in (20) are first imposedto found the vector 119870 in terms of the unknown parameters119861119895(119895 = 1 2 6) These constants are next calculated in terms
of the specific bending moment 1198720by satisfaction of the
global equilibrium conditions in (19a) (19b) and (19c)
0 01 02 03 04 05 06 07 08 09 1
0
10
20
30
minus40
minus30
minus20
minus10
120590
120590z120590xz
Goodsell and Pipes (2013)Goodsell and Pipes (2013)
yb
mdashPresent solutionmdashPresent solution
Figure 2 Interlaminar stresses along the 45∘
minus45∘ interface of
[45∘
minus45∘
]119904
laminate
Table 1 Engineering properties of unidirectional graphiteopoxy[28]
1198641
(GPa)1198642
= 1198643
(GPa)11986612
= 11986613
(GPa)11986623
(GPa) 12059212
= 12059213
12059223
132 108 565 338 024 059
4 Numerical Results and Discussions
In this part several numerical examples are shown for thedistribution of interlaminar stress All physical layers areassumed to be of equal thickness (=05mm)Themechanicalproperties of unidirectional graphiteepoxy T3005208 usedin this study are shown in Table 1 [28]
Also each physical ply is modeled as being made up of 12numerical layers within LWT (ie 119901 = 12) In addition thewidth thickness ratio (ie 2119887ℎ) is assumed to be equal to 10Furthermore the stress components are normalized as
120590119894119895=120590119894119895
1205900
(30)
where 1205900= 1198720119887ℎ2
Figure 2 shows the distribution of interlaminar normaland shear stresses along the width of [45∘minus45∘]
119904laminate
Good correspondence was found between the present resultsand the results obtained by Goodsell and Pipes [29] whichconfirms the accuracy of the present solution Figure 3 showsthe distribution of interlaminar stresses 120590
119911and 120590
119910119911along the
minus45∘
0∘ and 120590
119909119911along the 0
∘
90∘ interfaces of the general
[45∘
minus 45∘
0∘
90∘
30∘
minus 30∘
] laminate It is seen that theinterlaminar stresses show high stress gradient near the freeedge It is observed that the interlaminar stresses 120590
119911and 120590
119909119911
grow quickly near the free edge while being zero in the innerregion of the laminate Also the magnitude of the transverseshear stress 120590
119909119911is greater than that of transverse normal stress
120590119911 On the other hand 120590
119910119911rises toward the free edge and
decreases suddenly to zero at free edgeThe interlaminar normal stress 120590
119911along the 90∘0∘ inter-
face of the unsymmetric cross-ply [90∘
0∘
90∘
0∘
90∘
0∘
]
International Journal of Engineering Mathematics 7
0
0
01 02
02
03 04
04
05 06
06
07 08 09 1
minus02
minus04
minus06
minus08
120590
120590xz at z = 0
120590z at z = h6120590yz at z = h6
yb
Figure 3 Distribution of interlaminar stresses 120590119911
and 120590119910119911
alongthe minus45∘0∘ and 120590
119909119911
along the 0∘90∘ interfaces of the [45∘ minus 45∘0∘
90∘
30∘
minus30∘
] laminate
0 02 04 06 08 1yb
minus4
0
minus8
minus12
minus16
120590z
2bh = 502bh = 20
2bh = 102bh = 5
Figure 4 Distribution of the interlaminar normal stress 120590119911
alongthe 90∘0∘ interface of the laminate for various width-to-thicknessratios
laminate for various width-to-thickness ratios is demon-strated in Figure 4 It is observed that by decreasingthe width-to-thickness ratio the boundary-layer region canbe expanded towards the internal region of the laminate withits width being almost equal to the thickness of the laminateIt is seen that the magnitude of the interlaminar stress at thefree edge is not varied as the width-to-thickness ratio of thelaminate is changed In addition the highly localized natureof interlaminar stresses near and exactly at the free edges ofthe laminate is apparent
The distribution of interlaminar stresses along the0∘
90∘ and 90
∘
0∘ interfaces of the unsymmetric cross-ply
[0∘90∘0∘90∘] and [90∘0∘90∘0∘] laminates respectivelyare compared in Figure 5 It is seen that the maximuminterfacial value 120590
119911at the 0
∘
90∘ and 90
∘
0∘ interfaces take
place at the free edge Figure 6 shows the variation ofinterlaminar normal stress 120590
119911on through-the-thickness and
near the free edge of the angle-ply [45∘minus 45∘45∘minus 45∘]laminate as the free edge is approached It is observed that
120590z at z =h4120590z at z
120590yz
120590yz at z120590yz at z = h4
minus14minus12minus1
minus08minus06minus04minus02
0020406
0 02 04 06 08 1
= h4= h4
in [0∘90∘0∘90∘]
in [0∘90∘0∘90∘]
in [90∘0∘90∘0∘]in [90∘0∘90∘0∘]
yb
Figure 5 Distribution of interlaminar stresses along the 0∘
90∘
and 90∘
0∘ interfaces of the [0∘90∘0∘90∘] and [90∘0∘90∘0∘]
laminates respectively
minus1
minus05
0
05
1
minus200 minus150 minus100 minus50 0 50 100 150 200
zh
y = 094by = 096b
y = 099by = b
120590z
Figure 6 Variations of interlaminar normal stress 120590119911
through thethickness of the [45∘minus45∘45∘minus45∘] laminate for various width-to-thickness ratios
the maximum negative and positive values of 120590119911occur within
the top minus80∘ layer and the bottom 80
∘ layer at the free edge(ie 119910 = 119887) respectively It is also noticed that 120590
119911diminishes
away from the free edge as the interior region of the laminateis approached Moreover 120590
119911reduces by moving slightly away
from the free edge and its distribution becomes smootherThe variations of the interlaminar shear stress 120590
119910119911at 119910 =
119887 through the thickness of the [0∘
60∘
minus60∘
]119904laminate are
displayed in Figure 7 By increasing the number of numericallayers in each lamina 120590
119910119911becomes slightly closer to zero but
8 International Journal of Engineering Mathematics
minus15
minus1
minus05
0
05
1
15
minus20 minus10 0 10 20 30
zh
p = 20
p = 12
p = 8
120590yz
Figure 7 Variations of interlaminar shear stress 120590119910119911
on through-thickness of the [0∘60∘minus60∘]119904
laminate as a function of layer subdivisionnumber 119901
012
01
008
006
004
002
0
minus002
120590z
p = 30p = 20
p = 12p = 8
0 02 04 06 08 1
yb
Figure 8 Variations of interlaminar normal stress 120590119911
on through-thickness of the [minus15∘
90∘
90∘
minus15∘
] laminate as a function of layersubdivision number 119901
it never becomes zero It should be noted that increasing thenumber of subdivisions results in no convergence for 120590
119911and
120590119909119911
at interface-edge junction of two dissimilar layers Thenumerical values of these components (120590
119911and 120590
119909119911) continue
to grow as the number of sublayers increased Since thegeneralized stress resultants 119877119896
119910
instead of 120590119910119911
are forced todisappear at the free edge in LWT the numerical value of120590119910119911
may never become zero at the interface-edge intersection
(even by increasing the number of sublayers in each physicallayer)
The distribution of interlaminar normal stress 120590119911on
through thickness of the general [minus15∘90∘90∘minus15∘] lam-inate is displayed in Figure 8 It is noted that increasingthe number of numerical layers (119901) in each lamina has nosignificant effect on the values of the interlaminar stress 120590
119911
within the boundary-layer region of the laminate expect
International Journal of Engineering Mathematics 9
exactly at the free edge (ie 119910 = 119887) Furthermore theinterlaminar normal stress 120590
119911grows rapidly in the vicinity of
the free edge while being zero in the interior region of thelaminate
5 Conclusions
In the present paper analytical solutions are developed toanalyze the interlaminar stresses for different lay-up con-figurations in laminated composite plates subjected to thebending moment The solutions were obtained based onthe reduced elasticity displacement field for long laminatedplates It is found that the components of the displacementsfield are composed of two distinct parts signifying theglobal and local deformations within laminates The localdisplacement functions as well as the interlaminar stressesthrough the layers of the laminate were found by Reddyrsquoslayerwise theory (LWT)Thenumerical results based onLWTwere shown for the free-edge interlaminar stresses throughthe thickness and across the interfaces of various cross-plysymmetric angle-ply and general composite laminates
Appendix
The laminate rigidities in (22a) (22b) (22c) (22d) (24a)(24b) and (24c) are defined as
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
1206011015840
119895
1206011198961206011015840
119895
120601119896120601119895) d119911
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
120601119896 1206011015840
119896
119911 120601119896119911) d119911
(119896 119895 = 1 2 119873 + 1)
(119860119901119902 119861119901119902 119863119901119902) =
119873
sum
119894=1
int
119911119894+1
119911119894
119862(119894)
119901119902
(1 119911 1199112
) d119911
(A1)
which upon integration are presented in the following form
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
)
=
(minus
119862(119896minus1)
119901119902
ℎ119896minus1
minus
119862(119896minus1)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
6) if 119895 = 119896 minus 1
(
119862(119896minus1)
119901119902
ℎ119896minus1
+
119862(119896)
119901119902
ℎ119896
119862(119896minus1)
119901119902
2minus
119862(119896)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
3+
ℎ119896119862(119896)
119901119902
3) if 119895 = 119896
(minus
119862(119896)
119901119902
ℎ119896
119862(119896)
119901119902
2
ℎ119896119862(119896)
119901119902
6) if 119895 = 119896 + 1
(0 0 0) if 119895 lt 119896 minus 1 or 119895 gt 119896 + 1
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
)
=
(minus119862(1)
119901119902
ℎ1119862(1)
119901119902
2 119862(1)
119901119902
1199112
1
minus 1199112
2
2ℎ1
119862(1)
119901119902
ℎ1
[1199113
1
minus 1199113
2
3minus 1199112
1199112
1
minus 1199112
2
2]) if 119896 = 1
(minus119862(119896minus1)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2]) if 119896 = 119873 + 1
(119862(119896minus1)
119901119902
minus 119862(119896)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2+
ℎ119896119862(119896)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
+ 119862(119896)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2] +
119862(119896)
119901119902
ℎ119896
[1199113
119896
minus 1199113
119896+1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896+1
2]) if 1 lt 119896 lt 119873 + 1
(A2)
10 International Journal of Engineering Mathematics
Also
(119860119901119902 119861119901119902 119863119901119902)
=
119873
sum
119894=1
119862(119894)
119901119902
([119911119894+1
minus 119911119894] [
1199112
119894+1
minus 1199112
119894
2] [
1199113
119894+1
minus 1199113
119894
3])
(A3)
The coefficient matrices [119872] [119870] and [119871] appearing in(25) are given as
[119872] =[[
[
120575119878[11986366] 120575119878[11986326] 120575119878([11986136] minus [119861
45]119879
)
120575119878[11986326] [119863
22] [119861
23] minus [119861
44]119879
[0] [0] [11986344]
]]
]
[119870]=[
[
minus120575119878([11986055] + [120572]) minus120575
119878[11986045] [0]
minus120575119878[11986045] minus ([119860
44] + [120572]) [0]
120575119878([11986145]minus[11986136]119879
) [11986144]minus[11986123]119879
minus ([11986033]+[120572])
]
]
[119871] = [
[
12057511986011986055 0 0
12057511986011986045 0 0
minus120575119860(11986145 + 119861
36) 119860
13 12057511986211986113
]
]
(A4)
where [119860119901119902] [119861119901119902] and [119863
119901119902] are (119873 + 1) times (119873 + 1) square
matrices containing 119860119896119895119901119902 119861119896119895119901119902 and 119863
119896119895
119901119902 respectively and the
vectors 119860119901119902 119861119901119902 and 119861
119901119902 are (119873+1)times1 columnmatrices
containing 119860119896119901119902
119861119896119901119902
and 119861119896
119901119902
respectively Also [0] is (119873 +
1) times (119873 + 1) square zero and 0 is a zero vector with 119873 + 1
rows The artificial matrix [120572] is also an (119873 + 1) times (119873 + 1)
square matrix whose elements are given by
120572119896119895
= 120572int
ℎ2
minusℎ2
120601119896120601119895d119911 (A5)
with 120572 being a relatively small parameter in comparison withthe rigidity constants 119860119896119895
119901119902(119901119902 = 33 44 55) It is noted that
the insertion of [120572] in the matrix [119870] makes the eigenvaluesof the matrix (minus[119872]
minus1
[119870]) distinct
References
[1] T Kant and K Swaminathan ldquoEstimation of transverseinter-laminar stresses in laminated compositesmdasha selective reviewand survey of current developmentsrdquo Composite Structures vol49 no 1 pp 65ndash75 2000
[2] A H Puppo and H A Evensen ldquoInterlaminar shear ınlamınated composıtes under generalızed plane stressrdquo Journalof Composite Materials vol 4 pp 204ndash220 1970
[3] N J Pagano ldquoOn the calculatıon of ınterlamınar normal stressın composıte lamınaterdquo Journal of Composite Materials vol 8pp 65ndash81 1974
[4] P W Hsu and C T Herakovich ldquoEdge effects in angle-plycomposite laminatesrdquo Journal of CompositeMaterials vol 11 pp422ndash428 1977
[5] S Tang and A Levy ldquoBoundary layer theory 2 extension oflaminated finite striprdquo Journal of CompositeMaterials vol 9 no1 pp 42ndash52 1975
[6] R B Pipes andN J Pagano ldquoInterlaminar stresses in compositelaminates an approximate elasticity solutionrdquo Journal of AppliedMechanics vol 41 no 3 pp 668ndash672 1974
[7] N J Pagano ldquoStress fields in composite laminatesrdquo InternationalJournal of Solids and Structures vol 14 no 5 pp 385ndash400 1978
[8] S S Wang and I Choi ldquoBoundary-layer effects in composıtelaminates 1 free-edge stress singulaiıtiesrdquo Journal of AppliedMechanics vol V 49 no 3 pp 541ndash548 1982
[9] W L Yin ldquoFree-edge effects in anisotropic laminates underextension bending and twisting part I a stress-function-basedvariational approachrdquo Journal of Applied Mechanics vol 61 no2 pp 410ndash415 1994
[10] A S D Wang and F W Crossman ldquoSome new results on edgeeffect in symmetric composite laminatesrdquo Journal of CompositeMaterials vol 11 no 1 pp 92ndash106 1977
[11] J D Whitcomb I S Raju and J G Goree ldquoReliability ofthe finite element method for calculating free edge stresses incomposite laminatesrdquo Computers and Structures vol 15 no 1pp 23ndash37 1982
[12] G Davı ldquoStress fields in general composite laminatesrdquo AIAAJournal vol 34 no 12 pp 2604ndash2608 1996
[13] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT Part 1 derivationof finite element matricesrdquo International Journal for NumericalMethods in Engineering vol 55 no 2 pp 191ndash231 2002
[14] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT part 2 numericalimplementationsrdquo International Journal for Numerical Methodsin Engineering vol 55 no 3 pp 253ndash291 2002
[15] V-T Nguyen and J-F Caron ldquoFinite element analysis of free-edge stresses in composite laminates under mechanical anthermal loadingrdquo Composites Science and Technology vol 69no 1 pp 40ndash49 2009
[16] D H Robbins Jr and J N Reddy ldquoModelling of thick compos-ites using a layerwise laminate theoryrdquo International Journal forNumerical Methods in Engineering vol 36 no 4 pp 655ndash6771993
[17] C Mittelstedt and W Becker ldquoReddyrsquos layerwise laminate platetheory for the computation of elastic fields in the vicinity ofstraight free laminate edgesrdquoMaterials Science and EngineeringA vol 498 no 1-2 pp 76ndash80 2008
[18] W J Na Damage analysis of laminated composite beams underbending loads using the layer-wise theory [Dissertation thesis]Texas AampM University Texas Tex USA 2008
[19] T S Plagianakos and D A Saravanos ldquoHigher-order layerwiselaminate theory for the prediction of interlaminar shear stressesin thick composite and sandwich composite platesrdquo CompositeStructures vol 87 no 1 pp 23ndash35 2009
[20] H Ullah A R Harland T Lucas D Price and V V Sil-berschmidt ldquoFinite-element modelling of bending of CFRPlaminates multiple delaminationsrdquo Computational MaterialsScience vol 52 no 1 pp 147ndash156 2012
[21] F Helenon M R Wisnom S R Hallett and R S TraskldquoInvestigation into failure of laminated composite T-piecespecimens under bending loadingrdquo Composites A vol 54 pp182ndash189 2013
[22] C H Thai A J M Ferreira E Carrera and H Nguyen-XuanldquoIsogeometric analysis of laminated composite and sandwichplates using a layerwise deformation theoryrdquo Composite Struc-tures vol 104 pp 196ndash214 2013
International Journal of Engineering Mathematics 11
[23] N D Thai M DrsquoOttavio and J-F Caron ldquoBending analysis oflaminated and sandwich plates using a layer-wise stress modelrdquoComposite Structures vol 96 pp 135ndash142 2013
[24] PMalekzadeh ldquoA two-dimensional layerwise-differential quad-rature static analysis of thick laminated composite circulararchesrdquoAppliedMathematicalModelling vol 33 no 4 pp 1850ndash1861 2009
[25] Y C Fung and P Tong Classical and Computational SolidMechanics World Scientific New Jersey NJ USA 2001
[26] S G LekhnitskiiTheory of Elasticity of anAnisotropic BodyMirPublishers Moscow Russia 1981
[27] A Nosier R K Kapania and J N Reddy ldquoFree vibrationanalysis of laminated plates using a layerwise theoryrdquo AIAAJournal vol 31 no 12 pp 2335ndash2346 1993
[28] C T HerakovichMechanics of Fibrous Composites Wiley NewYork NY USA 1998
[29] O Goodsell and R B Pipes ldquoInterlaminar stresses in compositelaminates subjected to anticlastic bending deformationrdquo Journalof Applied Mechanics vol 80 no 4 pp 1ndash7 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
6 International Journal of Engineering Mathematics
1205751198612 int119887
minus119887
(120575119878119861119896
16
1198801015840
119895
+ 119861119896
12
1198811015840
119895
+ 119860119896
13
119882119895
minus 120575119860119861161198611+ 119860111198612+ 120575119862119861111198616) d119910 = 0
(24b)
1205751198616 120575119862int
119887
minus119887
(120575119878119863119896
16
1198801015840
119895
+ 119863119896
12
1198811015840
119895
+ 119861119896
13
119882119895
minus 120575119860119863161198611+ 119861111198612+ 120575119862119863111198616) d119910 = 119872
0
(24c)
where the extra laminate rigidities appearing in (24a) (24b)and (24c) are defined in the Appendix The system ofequations in (23a) (23b) and (23c) shows 3(119873 + 1) coupledordinary differential equations with constant coefficientswhich may be indicated in a matrix form as
[119872] 12057810158401015840
+ [119870] 120578 = [119871] 119861 sdot 119910 (25)
where
120578 = 119880119879
119881119879
119882119879
119879
119880 = 1198801 1198802 119880
119873+1119879
119881 = 1198811 1198812 119881
119873+1119879
119882 = 11988211198822 119882
119873+1119879
(26)
119861 = 1198611 1198612 1198616119879
119882119895= int
119910
119882119895d119910
(27)
The coefficient matrices [119872] [119870] and [119871] in (25) are dis-played in the Appendix Also from the conditions in (3) andthe displacement field in (23a) (23b) and (23c) it is observedthat the functions 119880
119895 119881119895 and119882
119895are all odd functions of the
independent variable 119910 It can be confirmed that the generalsolution of (25) may be presented as
120578 = [120595] [sinh (120582119910)] 119867 + [119870]minus1
[119871] 119861 sdot 119910 (28)
where [sinh(120582119910)] is a 3(119873 + 1) times 3(119873 + 1) diagonal matrixand
[sinh (120582119910)]
= diag (sinh (1205821119910) sinh (120582
2119910) sinh (120582
3(119873+1)119910))
(29)
Also [120595] and (1205822
1
1205822
2
1205822
3(119873+1)
) are the model matrixand eigenvalues of (minus[119872]
minus1
[119870]) respectively 119870 is anunknown vector representing 3(119873+1) integration constantsThe constants 119861
119895(119895 = 1 2 6)must be calculated within LWT
analysis So the boundary conditions in (20) are first imposedto found the vector 119870 in terms of the unknown parameters119861119895(119895 = 1 2 6) These constants are next calculated in terms
of the specific bending moment 1198720by satisfaction of the
global equilibrium conditions in (19a) (19b) and (19c)
0 01 02 03 04 05 06 07 08 09 1
0
10
20
30
minus40
minus30
minus20
minus10
120590
120590z120590xz
Goodsell and Pipes (2013)Goodsell and Pipes (2013)
yb
mdashPresent solutionmdashPresent solution
Figure 2 Interlaminar stresses along the 45∘
minus45∘ interface of
[45∘
minus45∘
]119904
laminate
Table 1 Engineering properties of unidirectional graphiteopoxy[28]
1198641
(GPa)1198642
= 1198643
(GPa)11986612
= 11986613
(GPa)11986623
(GPa) 12059212
= 12059213
12059223
132 108 565 338 024 059
4 Numerical Results and Discussions
In this part several numerical examples are shown for thedistribution of interlaminar stress All physical layers areassumed to be of equal thickness (=05mm)Themechanicalproperties of unidirectional graphiteepoxy T3005208 usedin this study are shown in Table 1 [28]
Also each physical ply is modeled as being made up of 12numerical layers within LWT (ie 119901 = 12) In addition thewidth thickness ratio (ie 2119887ℎ) is assumed to be equal to 10Furthermore the stress components are normalized as
120590119894119895=120590119894119895
1205900
(30)
where 1205900= 1198720119887ℎ2
Figure 2 shows the distribution of interlaminar normaland shear stresses along the width of [45∘minus45∘]
119904laminate
Good correspondence was found between the present resultsand the results obtained by Goodsell and Pipes [29] whichconfirms the accuracy of the present solution Figure 3 showsthe distribution of interlaminar stresses 120590
119911and 120590
119910119911along the
minus45∘
0∘ and 120590
119909119911along the 0
∘
90∘ interfaces of the general
[45∘
minus 45∘
0∘
90∘
30∘
minus 30∘
] laminate It is seen that theinterlaminar stresses show high stress gradient near the freeedge It is observed that the interlaminar stresses 120590
119911and 120590
119909119911
grow quickly near the free edge while being zero in the innerregion of the laminate Also the magnitude of the transverseshear stress 120590
119909119911is greater than that of transverse normal stress
120590119911 On the other hand 120590
119910119911rises toward the free edge and
decreases suddenly to zero at free edgeThe interlaminar normal stress 120590
119911along the 90∘0∘ inter-
face of the unsymmetric cross-ply [90∘
0∘
90∘
0∘
90∘
0∘
]
International Journal of Engineering Mathematics 7
0
0
01 02
02
03 04
04
05 06
06
07 08 09 1
minus02
minus04
minus06
minus08
120590
120590xz at z = 0
120590z at z = h6120590yz at z = h6
yb
Figure 3 Distribution of interlaminar stresses 120590119911
and 120590119910119911
alongthe minus45∘0∘ and 120590
119909119911
along the 0∘90∘ interfaces of the [45∘ minus 45∘0∘
90∘
30∘
minus30∘
] laminate
0 02 04 06 08 1yb
minus4
0
minus8
minus12
minus16
120590z
2bh = 502bh = 20
2bh = 102bh = 5
Figure 4 Distribution of the interlaminar normal stress 120590119911
alongthe 90∘0∘ interface of the laminate for various width-to-thicknessratios
laminate for various width-to-thickness ratios is demon-strated in Figure 4 It is observed that by decreasingthe width-to-thickness ratio the boundary-layer region canbe expanded towards the internal region of the laminate withits width being almost equal to the thickness of the laminateIt is seen that the magnitude of the interlaminar stress at thefree edge is not varied as the width-to-thickness ratio of thelaminate is changed In addition the highly localized natureof interlaminar stresses near and exactly at the free edges ofthe laminate is apparent
The distribution of interlaminar stresses along the0∘
90∘ and 90
∘
0∘ interfaces of the unsymmetric cross-ply
[0∘90∘0∘90∘] and [90∘0∘90∘0∘] laminates respectivelyare compared in Figure 5 It is seen that the maximuminterfacial value 120590
119911at the 0
∘
90∘ and 90
∘
0∘ interfaces take
place at the free edge Figure 6 shows the variation ofinterlaminar normal stress 120590
119911on through-the-thickness and
near the free edge of the angle-ply [45∘minus 45∘45∘minus 45∘]laminate as the free edge is approached It is observed that
120590z at z =h4120590z at z
120590yz
120590yz at z120590yz at z = h4
minus14minus12minus1
minus08minus06minus04minus02
0020406
0 02 04 06 08 1
= h4= h4
in [0∘90∘0∘90∘]
in [0∘90∘0∘90∘]
in [90∘0∘90∘0∘]in [90∘0∘90∘0∘]
yb
Figure 5 Distribution of interlaminar stresses along the 0∘
90∘
and 90∘
0∘ interfaces of the [0∘90∘0∘90∘] and [90∘0∘90∘0∘]
laminates respectively
minus1
minus05
0
05
1
minus200 minus150 minus100 minus50 0 50 100 150 200
zh
y = 094by = 096b
y = 099by = b
120590z
Figure 6 Variations of interlaminar normal stress 120590119911
through thethickness of the [45∘minus45∘45∘minus45∘] laminate for various width-to-thickness ratios
the maximum negative and positive values of 120590119911occur within
the top minus80∘ layer and the bottom 80
∘ layer at the free edge(ie 119910 = 119887) respectively It is also noticed that 120590
119911diminishes
away from the free edge as the interior region of the laminateis approached Moreover 120590
119911reduces by moving slightly away
from the free edge and its distribution becomes smootherThe variations of the interlaminar shear stress 120590
119910119911at 119910 =
119887 through the thickness of the [0∘
60∘
minus60∘
]119904laminate are
displayed in Figure 7 By increasing the number of numericallayers in each lamina 120590
119910119911becomes slightly closer to zero but
8 International Journal of Engineering Mathematics
minus15
minus1
minus05
0
05
1
15
minus20 minus10 0 10 20 30
zh
p = 20
p = 12
p = 8
120590yz
Figure 7 Variations of interlaminar shear stress 120590119910119911
on through-thickness of the [0∘60∘minus60∘]119904
laminate as a function of layer subdivisionnumber 119901
012
01
008
006
004
002
0
minus002
120590z
p = 30p = 20
p = 12p = 8
0 02 04 06 08 1
yb
Figure 8 Variations of interlaminar normal stress 120590119911
on through-thickness of the [minus15∘
90∘
90∘
minus15∘
] laminate as a function of layersubdivision number 119901
it never becomes zero It should be noted that increasing thenumber of subdivisions results in no convergence for 120590
119911and
120590119909119911
at interface-edge junction of two dissimilar layers Thenumerical values of these components (120590
119911and 120590
119909119911) continue
to grow as the number of sublayers increased Since thegeneralized stress resultants 119877119896
119910
instead of 120590119910119911
are forced todisappear at the free edge in LWT the numerical value of120590119910119911
may never become zero at the interface-edge intersection
(even by increasing the number of sublayers in each physicallayer)
The distribution of interlaminar normal stress 120590119911on
through thickness of the general [minus15∘90∘90∘minus15∘] lam-inate is displayed in Figure 8 It is noted that increasingthe number of numerical layers (119901) in each lamina has nosignificant effect on the values of the interlaminar stress 120590
119911
within the boundary-layer region of the laminate expect
International Journal of Engineering Mathematics 9
exactly at the free edge (ie 119910 = 119887) Furthermore theinterlaminar normal stress 120590
119911grows rapidly in the vicinity of
the free edge while being zero in the interior region of thelaminate
5 Conclusions
In the present paper analytical solutions are developed toanalyze the interlaminar stresses for different lay-up con-figurations in laminated composite plates subjected to thebending moment The solutions were obtained based onthe reduced elasticity displacement field for long laminatedplates It is found that the components of the displacementsfield are composed of two distinct parts signifying theglobal and local deformations within laminates The localdisplacement functions as well as the interlaminar stressesthrough the layers of the laminate were found by Reddyrsquoslayerwise theory (LWT)Thenumerical results based onLWTwere shown for the free-edge interlaminar stresses throughthe thickness and across the interfaces of various cross-plysymmetric angle-ply and general composite laminates
Appendix
The laminate rigidities in (22a) (22b) (22c) (22d) (24a)(24b) and (24c) are defined as
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
1206011015840
119895
1206011198961206011015840
119895
120601119896120601119895) d119911
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
120601119896 1206011015840
119896
119911 120601119896119911) d119911
(119896 119895 = 1 2 119873 + 1)
(119860119901119902 119861119901119902 119863119901119902) =
119873
sum
119894=1
int
119911119894+1
119911119894
119862(119894)
119901119902
(1 119911 1199112
) d119911
(A1)
which upon integration are presented in the following form
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
)
=
(minus
119862(119896minus1)
119901119902
ℎ119896minus1
minus
119862(119896minus1)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
6) if 119895 = 119896 minus 1
(
119862(119896minus1)
119901119902
ℎ119896minus1
+
119862(119896)
119901119902
ℎ119896
119862(119896minus1)
119901119902
2minus
119862(119896)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
3+
ℎ119896119862(119896)
119901119902
3) if 119895 = 119896
(minus
119862(119896)
119901119902
ℎ119896
119862(119896)
119901119902
2
ℎ119896119862(119896)
119901119902
6) if 119895 = 119896 + 1
(0 0 0) if 119895 lt 119896 minus 1 or 119895 gt 119896 + 1
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
)
=
(minus119862(1)
119901119902
ℎ1119862(1)
119901119902
2 119862(1)
119901119902
1199112
1
minus 1199112
2
2ℎ1
119862(1)
119901119902
ℎ1
[1199113
1
minus 1199113
2
3minus 1199112
1199112
1
minus 1199112
2
2]) if 119896 = 1
(minus119862(119896minus1)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2]) if 119896 = 119873 + 1
(119862(119896minus1)
119901119902
minus 119862(119896)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2+
ℎ119896119862(119896)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
+ 119862(119896)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2] +
119862(119896)
119901119902
ℎ119896
[1199113
119896
minus 1199113
119896+1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896+1
2]) if 1 lt 119896 lt 119873 + 1
(A2)
10 International Journal of Engineering Mathematics
Also
(119860119901119902 119861119901119902 119863119901119902)
=
119873
sum
119894=1
119862(119894)
119901119902
([119911119894+1
minus 119911119894] [
1199112
119894+1
minus 1199112
119894
2] [
1199113
119894+1
minus 1199113
119894
3])
(A3)
The coefficient matrices [119872] [119870] and [119871] appearing in(25) are given as
[119872] =[[
[
120575119878[11986366] 120575119878[11986326] 120575119878([11986136] minus [119861
45]119879
)
120575119878[11986326] [119863
22] [119861
23] minus [119861
44]119879
[0] [0] [11986344]
]]
]
[119870]=[
[
minus120575119878([11986055] + [120572]) minus120575
119878[11986045] [0]
minus120575119878[11986045] minus ([119860
44] + [120572]) [0]
120575119878([11986145]minus[11986136]119879
) [11986144]minus[11986123]119879
minus ([11986033]+[120572])
]
]
[119871] = [
[
12057511986011986055 0 0
12057511986011986045 0 0
minus120575119860(11986145 + 119861
36) 119860
13 12057511986211986113
]
]
(A4)
where [119860119901119902] [119861119901119902] and [119863
119901119902] are (119873 + 1) times (119873 + 1) square
matrices containing 119860119896119895119901119902 119861119896119895119901119902 and 119863
119896119895
119901119902 respectively and the
vectors 119860119901119902 119861119901119902 and 119861
119901119902 are (119873+1)times1 columnmatrices
containing 119860119896119901119902
119861119896119901119902
and 119861119896
119901119902
respectively Also [0] is (119873 +
1) times (119873 + 1) square zero and 0 is a zero vector with 119873 + 1
rows The artificial matrix [120572] is also an (119873 + 1) times (119873 + 1)
square matrix whose elements are given by
120572119896119895
= 120572int
ℎ2
minusℎ2
120601119896120601119895d119911 (A5)
with 120572 being a relatively small parameter in comparison withthe rigidity constants 119860119896119895
119901119902(119901119902 = 33 44 55) It is noted that
the insertion of [120572] in the matrix [119870] makes the eigenvaluesof the matrix (minus[119872]
minus1
[119870]) distinct
References
[1] T Kant and K Swaminathan ldquoEstimation of transverseinter-laminar stresses in laminated compositesmdasha selective reviewand survey of current developmentsrdquo Composite Structures vol49 no 1 pp 65ndash75 2000
[2] A H Puppo and H A Evensen ldquoInterlaminar shear ınlamınated composıtes under generalızed plane stressrdquo Journalof Composite Materials vol 4 pp 204ndash220 1970
[3] N J Pagano ldquoOn the calculatıon of ınterlamınar normal stressın composıte lamınaterdquo Journal of Composite Materials vol 8pp 65ndash81 1974
[4] P W Hsu and C T Herakovich ldquoEdge effects in angle-plycomposite laminatesrdquo Journal of CompositeMaterials vol 11 pp422ndash428 1977
[5] S Tang and A Levy ldquoBoundary layer theory 2 extension oflaminated finite striprdquo Journal of CompositeMaterials vol 9 no1 pp 42ndash52 1975
[6] R B Pipes andN J Pagano ldquoInterlaminar stresses in compositelaminates an approximate elasticity solutionrdquo Journal of AppliedMechanics vol 41 no 3 pp 668ndash672 1974
[7] N J Pagano ldquoStress fields in composite laminatesrdquo InternationalJournal of Solids and Structures vol 14 no 5 pp 385ndash400 1978
[8] S S Wang and I Choi ldquoBoundary-layer effects in composıtelaminates 1 free-edge stress singulaiıtiesrdquo Journal of AppliedMechanics vol V 49 no 3 pp 541ndash548 1982
[9] W L Yin ldquoFree-edge effects in anisotropic laminates underextension bending and twisting part I a stress-function-basedvariational approachrdquo Journal of Applied Mechanics vol 61 no2 pp 410ndash415 1994
[10] A S D Wang and F W Crossman ldquoSome new results on edgeeffect in symmetric composite laminatesrdquo Journal of CompositeMaterials vol 11 no 1 pp 92ndash106 1977
[11] J D Whitcomb I S Raju and J G Goree ldquoReliability ofthe finite element method for calculating free edge stresses incomposite laminatesrdquo Computers and Structures vol 15 no 1pp 23ndash37 1982
[12] G Davı ldquoStress fields in general composite laminatesrdquo AIAAJournal vol 34 no 12 pp 2604ndash2608 1996
[13] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT Part 1 derivationof finite element matricesrdquo International Journal for NumericalMethods in Engineering vol 55 no 2 pp 191ndash231 2002
[14] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT part 2 numericalimplementationsrdquo International Journal for Numerical Methodsin Engineering vol 55 no 3 pp 253ndash291 2002
[15] V-T Nguyen and J-F Caron ldquoFinite element analysis of free-edge stresses in composite laminates under mechanical anthermal loadingrdquo Composites Science and Technology vol 69no 1 pp 40ndash49 2009
[16] D H Robbins Jr and J N Reddy ldquoModelling of thick compos-ites using a layerwise laminate theoryrdquo International Journal forNumerical Methods in Engineering vol 36 no 4 pp 655ndash6771993
[17] C Mittelstedt and W Becker ldquoReddyrsquos layerwise laminate platetheory for the computation of elastic fields in the vicinity ofstraight free laminate edgesrdquoMaterials Science and EngineeringA vol 498 no 1-2 pp 76ndash80 2008
[18] W J Na Damage analysis of laminated composite beams underbending loads using the layer-wise theory [Dissertation thesis]Texas AampM University Texas Tex USA 2008
[19] T S Plagianakos and D A Saravanos ldquoHigher-order layerwiselaminate theory for the prediction of interlaminar shear stressesin thick composite and sandwich composite platesrdquo CompositeStructures vol 87 no 1 pp 23ndash35 2009
[20] H Ullah A R Harland T Lucas D Price and V V Sil-berschmidt ldquoFinite-element modelling of bending of CFRPlaminates multiple delaminationsrdquo Computational MaterialsScience vol 52 no 1 pp 147ndash156 2012
[21] F Helenon M R Wisnom S R Hallett and R S TraskldquoInvestigation into failure of laminated composite T-piecespecimens under bending loadingrdquo Composites A vol 54 pp182ndash189 2013
[22] C H Thai A J M Ferreira E Carrera and H Nguyen-XuanldquoIsogeometric analysis of laminated composite and sandwichplates using a layerwise deformation theoryrdquo Composite Struc-tures vol 104 pp 196ndash214 2013
International Journal of Engineering Mathematics 11
[23] N D Thai M DrsquoOttavio and J-F Caron ldquoBending analysis oflaminated and sandwich plates using a layer-wise stress modelrdquoComposite Structures vol 96 pp 135ndash142 2013
[24] PMalekzadeh ldquoA two-dimensional layerwise-differential quad-rature static analysis of thick laminated composite circulararchesrdquoAppliedMathematicalModelling vol 33 no 4 pp 1850ndash1861 2009
[25] Y C Fung and P Tong Classical and Computational SolidMechanics World Scientific New Jersey NJ USA 2001
[26] S G LekhnitskiiTheory of Elasticity of anAnisotropic BodyMirPublishers Moscow Russia 1981
[27] A Nosier R K Kapania and J N Reddy ldquoFree vibrationanalysis of laminated plates using a layerwise theoryrdquo AIAAJournal vol 31 no 12 pp 2335ndash2346 1993
[28] C T HerakovichMechanics of Fibrous Composites Wiley NewYork NY USA 1998
[29] O Goodsell and R B Pipes ldquoInterlaminar stresses in compositelaminates subjected to anticlastic bending deformationrdquo Journalof Applied Mechanics vol 80 no 4 pp 1ndash7 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
International Journal of Engineering Mathematics 7
0
0
01 02
02
03 04
04
05 06
06
07 08 09 1
minus02
minus04
minus06
minus08
120590
120590xz at z = 0
120590z at z = h6120590yz at z = h6
yb
Figure 3 Distribution of interlaminar stresses 120590119911
and 120590119910119911
alongthe minus45∘0∘ and 120590
119909119911
along the 0∘90∘ interfaces of the [45∘ minus 45∘0∘
90∘
30∘
minus30∘
] laminate
0 02 04 06 08 1yb
minus4
0
minus8
minus12
minus16
120590z
2bh = 502bh = 20
2bh = 102bh = 5
Figure 4 Distribution of the interlaminar normal stress 120590119911
alongthe 90∘0∘ interface of the laminate for various width-to-thicknessratios
laminate for various width-to-thickness ratios is demon-strated in Figure 4 It is observed that by decreasingthe width-to-thickness ratio the boundary-layer region canbe expanded towards the internal region of the laminate withits width being almost equal to the thickness of the laminateIt is seen that the magnitude of the interlaminar stress at thefree edge is not varied as the width-to-thickness ratio of thelaminate is changed In addition the highly localized natureof interlaminar stresses near and exactly at the free edges ofthe laminate is apparent
The distribution of interlaminar stresses along the0∘
90∘ and 90
∘
0∘ interfaces of the unsymmetric cross-ply
[0∘90∘0∘90∘] and [90∘0∘90∘0∘] laminates respectivelyare compared in Figure 5 It is seen that the maximuminterfacial value 120590
119911at the 0
∘
90∘ and 90
∘
0∘ interfaces take
place at the free edge Figure 6 shows the variation ofinterlaminar normal stress 120590
119911on through-the-thickness and
near the free edge of the angle-ply [45∘minus 45∘45∘minus 45∘]laminate as the free edge is approached It is observed that
120590z at z =h4120590z at z
120590yz
120590yz at z120590yz at z = h4
minus14minus12minus1
minus08minus06minus04minus02
0020406
0 02 04 06 08 1
= h4= h4
in [0∘90∘0∘90∘]
in [0∘90∘0∘90∘]
in [90∘0∘90∘0∘]in [90∘0∘90∘0∘]
yb
Figure 5 Distribution of interlaminar stresses along the 0∘
90∘
and 90∘
0∘ interfaces of the [0∘90∘0∘90∘] and [90∘0∘90∘0∘]
laminates respectively
minus1
minus05
0
05
1
minus200 minus150 minus100 minus50 0 50 100 150 200
zh
y = 094by = 096b
y = 099by = b
120590z
Figure 6 Variations of interlaminar normal stress 120590119911
through thethickness of the [45∘minus45∘45∘minus45∘] laminate for various width-to-thickness ratios
the maximum negative and positive values of 120590119911occur within
the top minus80∘ layer and the bottom 80
∘ layer at the free edge(ie 119910 = 119887) respectively It is also noticed that 120590
119911diminishes
away from the free edge as the interior region of the laminateis approached Moreover 120590
119911reduces by moving slightly away
from the free edge and its distribution becomes smootherThe variations of the interlaminar shear stress 120590
119910119911at 119910 =
119887 through the thickness of the [0∘
60∘
minus60∘
]119904laminate are
displayed in Figure 7 By increasing the number of numericallayers in each lamina 120590
119910119911becomes slightly closer to zero but
8 International Journal of Engineering Mathematics
minus15
minus1
minus05
0
05
1
15
minus20 minus10 0 10 20 30
zh
p = 20
p = 12
p = 8
120590yz
Figure 7 Variations of interlaminar shear stress 120590119910119911
on through-thickness of the [0∘60∘minus60∘]119904
laminate as a function of layer subdivisionnumber 119901
012
01
008
006
004
002
0
minus002
120590z
p = 30p = 20
p = 12p = 8
0 02 04 06 08 1
yb
Figure 8 Variations of interlaminar normal stress 120590119911
on through-thickness of the [minus15∘
90∘
90∘
minus15∘
] laminate as a function of layersubdivision number 119901
it never becomes zero It should be noted that increasing thenumber of subdivisions results in no convergence for 120590
119911and
120590119909119911
at interface-edge junction of two dissimilar layers Thenumerical values of these components (120590
119911and 120590
119909119911) continue
to grow as the number of sublayers increased Since thegeneralized stress resultants 119877119896
119910
instead of 120590119910119911
are forced todisappear at the free edge in LWT the numerical value of120590119910119911
may never become zero at the interface-edge intersection
(even by increasing the number of sublayers in each physicallayer)
The distribution of interlaminar normal stress 120590119911on
through thickness of the general [minus15∘90∘90∘minus15∘] lam-inate is displayed in Figure 8 It is noted that increasingthe number of numerical layers (119901) in each lamina has nosignificant effect on the values of the interlaminar stress 120590
119911
within the boundary-layer region of the laminate expect
International Journal of Engineering Mathematics 9
exactly at the free edge (ie 119910 = 119887) Furthermore theinterlaminar normal stress 120590
119911grows rapidly in the vicinity of
the free edge while being zero in the interior region of thelaminate
5 Conclusions
In the present paper analytical solutions are developed toanalyze the interlaminar stresses for different lay-up con-figurations in laminated composite plates subjected to thebending moment The solutions were obtained based onthe reduced elasticity displacement field for long laminatedplates It is found that the components of the displacementsfield are composed of two distinct parts signifying theglobal and local deformations within laminates The localdisplacement functions as well as the interlaminar stressesthrough the layers of the laminate were found by Reddyrsquoslayerwise theory (LWT)Thenumerical results based onLWTwere shown for the free-edge interlaminar stresses throughthe thickness and across the interfaces of various cross-plysymmetric angle-ply and general composite laminates
Appendix
The laminate rigidities in (22a) (22b) (22c) (22d) (24a)(24b) and (24c) are defined as
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
1206011015840
119895
1206011198961206011015840
119895
120601119896120601119895) d119911
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
120601119896 1206011015840
119896
119911 120601119896119911) d119911
(119896 119895 = 1 2 119873 + 1)
(119860119901119902 119861119901119902 119863119901119902) =
119873
sum
119894=1
int
119911119894+1
119911119894
119862(119894)
119901119902
(1 119911 1199112
) d119911
(A1)
which upon integration are presented in the following form
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
)
=
(minus
119862(119896minus1)
119901119902
ℎ119896minus1
minus
119862(119896minus1)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
6) if 119895 = 119896 minus 1
(
119862(119896minus1)
119901119902
ℎ119896minus1
+
119862(119896)
119901119902
ℎ119896
119862(119896minus1)
119901119902
2minus
119862(119896)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
3+
ℎ119896119862(119896)
119901119902
3) if 119895 = 119896
(minus
119862(119896)
119901119902
ℎ119896
119862(119896)
119901119902
2
ℎ119896119862(119896)
119901119902
6) if 119895 = 119896 + 1
(0 0 0) if 119895 lt 119896 minus 1 or 119895 gt 119896 + 1
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
)
=
(minus119862(1)
119901119902
ℎ1119862(1)
119901119902
2 119862(1)
119901119902
1199112
1
minus 1199112
2
2ℎ1
119862(1)
119901119902
ℎ1
[1199113
1
minus 1199113
2
3minus 1199112
1199112
1
minus 1199112
2
2]) if 119896 = 1
(minus119862(119896minus1)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2]) if 119896 = 119873 + 1
(119862(119896minus1)
119901119902
minus 119862(119896)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2+
ℎ119896119862(119896)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
+ 119862(119896)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2] +
119862(119896)
119901119902
ℎ119896
[1199113
119896
minus 1199113
119896+1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896+1
2]) if 1 lt 119896 lt 119873 + 1
(A2)
10 International Journal of Engineering Mathematics
Also
(119860119901119902 119861119901119902 119863119901119902)
=
119873
sum
119894=1
119862(119894)
119901119902
([119911119894+1
minus 119911119894] [
1199112
119894+1
minus 1199112
119894
2] [
1199113
119894+1
minus 1199113
119894
3])
(A3)
The coefficient matrices [119872] [119870] and [119871] appearing in(25) are given as
[119872] =[[
[
120575119878[11986366] 120575119878[11986326] 120575119878([11986136] minus [119861
45]119879
)
120575119878[11986326] [119863
22] [119861
23] minus [119861
44]119879
[0] [0] [11986344]
]]
]
[119870]=[
[
minus120575119878([11986055] + [120572]) minus120575
119878[11986045] [0]
minus120575119878[11986045] minus ([119860
44] + [120572]) [0]
120575119878([11986145]minus[11986136]119879
) [11986144]minus[11986123]119879
minus ([11986033]+[120572])
]
]
[119871] = [
[
12057511986011986055 0 0
12057511986011986045 0 0
minus120575119860(11986145 + 119861
36) 119860
13 12057511986211986113
]
]
(A4)
where [119860119901119902] [119861119901119902] and [119863
119901119902] are (119873 + 1) times (119873 + 1) square
matrices containing 119860119896119895119901119902 119861119896119895119901119902 and 119863
119896119895
119901119902 respectively and the
vectors 119860119901119902 119861119901119902 and 119861
119901119902 are (119873+1)times1 columnmatrices
containing 119860119896119901119902
119861119896119901119902
and 119861119896
119901119902
respectively Also [0] is (119873 +
1) times (119873 + 1) square zero and 0 is a zero vector with 119873 + 1
rows The artificial matrix [120572] is also an (119873 + 1) times (119873 + 1)
square matrix whose elements are given by
120572119896119895
= 120572int
ℎ2
minusℎ2
120601119896120601119895d119911 (A5)
with 120572 being a relatively small parameter in comparison withthe rigidity constants 119860119896119895
119901119902(119901119902 = 33 44 55) It is noted that
the insertion of [120572] in the matrix [119870] makes the eigenvaluesof the matrix (minus[119872]
minus1
[119870]) distinct
References
[1] T Kant and K Swaminathan ldquoEstimation of transverseinter-laminar stresses in laminated compositesmdasha selective reviewand survey of current developmentsrdquo Composite Structures vol49 no 1 pp 65ndash75 2000
[2] A H Puppo and H A Evensen ldquoInterlaminar shear ınlamınated composıtes under generalızed plane stressrdquo Journalof Composite Materials vol 4 pp 204ndash220 1970
[3] N J Pagano ldquoOn the calculatıon of ınterlamınar normal stressın composıte lamınaterdquo Journal of Composite Materials vol 8pp 65ndash81 1974
[4] P W Hsu and C T Herakovich ldquoEdge effects in angle-plycomposite laminatesrdquo Journal of CompositeMaterials vol 11 pp422ndash428 1977
[5] S Tang and A Levy ldquoBoundary layer theory 2 extension oflaminated finite striprdquo Journal of CompositeMaterials vol 9 no1 pp 42ndash52 1975
[6] R B Pipes andN J Pagano ldquoInterlaminar stresses in compositelaminates an approximate elasticity solutionrdquo Journal of AppliedMechanics vol 41 no 3 pp 668ndash672 1974
[7] N J Pagano ldquoStress fields in composite laminatesrdquo InternationalJournal of Solids and Structures vol 14 no 5 pp 385ndash400 1978
[8] S S Wang and I Choi ldquoBoundary-layer effects in composıtelaminates 1 free-edge stress singulaiıtiesrdquo Journal of AppliedMechanics vol V 49 no 3 pp 541ndash548 1982
[9] W L Yin ldquoFree-edge effects in anisotropic laminates underextension bending and twisting part I a stress-function-basedvariational approachrdquo Journal of Applied Mechanics vol 61 no2 pp 410ndash415 1994
[10] A S D Wang and F W Crossman ldquoSome new results on edgeeffect in symmetric composite laminatesrdquo Journal of CompositeMaterials vol 11 no 1 pp 92ndash106 1977
[11] J D Whitcomb I S Raju and J G Goree ldquoReliability ofthe finite element method for calculating free edge stresses incomposite laminatesrdquo Computers and Structures vol 15 no 1pp 23ndash37 1982
[12] G Davı ldquoStress fields in general composite laminatesrdquo AIAAJournal vol 34 no 12 pp 2604ndash2608 1996
[13] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT Part 1 derivationof finite element matricesrdquo International Journal for NumericalMethods in Engineering vol 55 no 2 pp 191ndash231 2002
[14] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT part 2 numericalimplementationsrdquo International Journal for Numerical Methodsin Engineering vol 55 no 3 pp 253ndash291 2002
[15] V-T Nguyen and J-F Caron ldquoFinite element analysis of free-edge stresses in composite laminates under mechanical anthermal loadingrdquo Composites Science and Technology vol 69no 1 pp 40ndash49 2009
[16] D H Robbins Jr and J N Reddy ldquoModelling of thick compos-ites using a layerwise laminate theoryrdquo International Journal forNumerical Methods in Engineering vol 36 no 4 pp 655ndash6771993
[17] C Mittelstedt and W Becker ldquoReddyrsquos layerwise laminate platetheory for the computation of elastic fields in the vicinity ofstraight free laminate edgesrdquoMaterials Science and EngineeringA vol 498 no 1-2 pp 76ndash80 2008
[18] W J Na Damage analysis of laminated composite beams underbending loads using the layer-wise theory [Dissertation thesis]Texas AampM University Texas Tex USA 2008
[19] T S Plagianakos and D A Saravanos ldquoHigher-order layerwiselaminate theory for the prediction of interlaminar shear stressesin thick composite and sandwich composite platesrdquo CompositeStructures vol 87 no 1 pp 23ndash35 2009
[20] H Ullah A R Harland T Lucas D Price and V V Sil-berschmidt ldquoFinite-element modelling of bending of CFRPlaminates multiple delaminationsrdquo Computational MaterialsScience vol 52 no 1 pp 147ndash156 2012
[21] F Helenon M R Wisnom S R Hallett and R S TraskldquoInvestigation into failure of laminated composite T-piecespecimens under bending loadingrdquo Composites A vol 54 pp182ndash189 2013
[22] C H Thai A J M Ferreira E Carrera and H Nguyen-XuanldquoIsogeometric analysis of laminated composite and sandwichplates using a layerwise deformation theoryrdquo Composite Struc-tures vol 104 pp 196ndash214 2013
International Journal of Engineering Mathematics 11
[23] N D Thai M DrsquoOttavio and J-F Caron ldquoBending analysis oflaminated and sandwich plates using a layer-wise stress modelrdquoComposite Structures vol 96 pp 135ndash142 2013
[24] PMalekzadeh ldquoA two-dimensional layerwise-differential quad-rature static analysis of thick laminated composite circulararchesrdquoAppliedMathematicalModelling vol 33 no 4 pp 1850ndash1861 2009
[25] Y C Fung and P Tong Classical and Computational SolidMechanics World Scientific New Jersey NJ USA 2001
[26] S G LekhnitskiiTheory of Elasticity of anAnisotropic BodyMirPublishers Moscow Russia 1981
[27] A Nosier R K Kapania and J N Reddy ldquoFree vibrationanalysis of laminated plates using a layerwise theoryrdquo AIAAJournal vol 31 no 12 pp 2335ndash2346 1993
[28] C T HerakovichMechanics of Fibrous Composites Wiley NewYork NY USA 1998
[29] O Goodsell and R B Pipes ldquoInterlaminar stresses in compositelaminates subjected to anticlastic bending deformationrdquo Journalof Applied Mechanics vol 80 no 4 pp 1ndash7 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
8 International Journal of Engineering Mathematics
minus15
minus1
minus05
0
05
1
15
minus20 minus10 0 10 20 30
zh
p = 20
p = 12
p = 8
120590yz
Figure 7 Variations of interlaminar shear stress 120590119910119911
on through-thickness of the [0∘60∘minus60∘]119904
laminate as a function of layer subdivisionnumber 119901
012
01
008
006
004
002
0
minus002
120590z
p = 30p = 20
p = 12p = 8
0 02 04 06 08 1
yb
Figure 8 Variations of interlaminar normal stress 120590119911
on through-thickness of the [minus15∘
90∘
90∘
minus15∘
] laminate as a function of layersubdivision number 119901
it never becomes zero It should be noted that increasing thenumber of subdivisions results in no convergence for 120590
119911and
120590119909119911
at interface-edge junction of two dissimilar layers Thenumerical values of these components (120590
119911and 120590
119909119911) continue
to grow as the number of sublayers increased Since thegeneralized stress resultants 119877119896
119910
instead of 120590119910119911
are forced todisappear at the free edge in LWT the numerical value of120590119910119911
may never become zero at the interface-edge intersection
(even by increasing the number of sublayers in each physicallayer)
The distribution of interlaminar normal stress 120590119911on
through thickness of the general [minus15∘90∘90∘minus15∘] lam-inate is displayed in Figure 8 It is noted that increasingthe number of numerical layers (119901) in each lamina has nosignificant effect on the values of the interlaminar stress 120590
119911
within the boundary-layer region of the laminate expect
International Journal of Engineering Mathematics 9
exactly at the free edge (ie 119910 = 119887) Furthermore theinterlaminar normal stress 120590
119911grows rapidly in the vicinity of
the free edge while being zero in the interior region of thelaminate
5 Conclusions
In the present paper analytical solutions are developed toanalyze the interlaminar stresses for different lay-up con-figurations in laminated composite plates subjected to thebending moment The solutions were obtained based onthe reduced elasticity displacement field for long laminatedplates It is found that the components of the displacementsfield are composed of two distinct parts signifying theglobal and local deformations within laminates The localdisplacement functions as well as the interlaminar stressesthrough the layers of the laminate were found by Reddyrsquoslayerwise theory (LWT)Thenumerical results based onLWTwere shown for the free-edge interlaminar stresses throughthe thickness and across the interfaces of various cross-plysymmetric angle-ply and general composite laminates
Appendix
The laminate rigidities in (22a) (22b) (22c) (22d) (24a)(24b) and (24c) are defined as
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
1206011015840
119895
1206011198961206011015840
119895
120601119896120601119895) d119911
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
120601119896 1206011015840
119896
119911 120601119896119911) d119911
(119896 119895 = 1 2 119873 + 1)
(119860119901119902 119861119901119902 119863119901119902) =
119873
sum
119894=1
int
119911119894+1
119911119894
119862(119894)
119901119902
(1 119911 1199112
) d119911
(A1)
which upon integration are presented in the following form
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
)
=
(minus
119862(119896minus1)
119901119902
ℎ119896minus1
minus
119862(119896minus1)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
6) if 119895 = 119896 minus 1
(
119862(119896minus1)
119901119902
ℎ119896minus1
+
119862(119896)
119901119902
ℎ119896
119862(119896minus1)
119901119902
2minus
119862(119896)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
3+
ℎ119896119862(119896)
119901119902
3) if 119895 = 119896
(minus
119862(119896)
119901119902
ℎ119896
119862(119896)
119901119902
2
ℎ119896119862(119896)
119901119902
6) if 119895 = 119896 + 1
(0 0 0) if 119895 lt 119896 minus 1 or 119895 gt 119896 + 1
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
)
=
(minus119862(1)
119901119902
ℎ1119862(1)
119901119902
2 119862(1)
119901119902
1199112
1
minus 1199112
2
2ℎ1
119862(1)
119901119902
ℎ1
[1199113
1
minus 1199113
2
3minus 1199112
1199112
1
minus 1199112
2
2]) if 119896 = 1
(minus119862(119896minus1)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2]) if 119896 = 119873 + 1
(119862(119896minus1)
119901119902
minus 119862(119896)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2+
ℎ119896119862(119896)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
+ 119862(119896)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2] +
119862(119896)
119901119902
ℎ119896
[1199113
119896
minus 1199113
119896+1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896+1
2]) if 1 lt 119896 lt 119873 + 1
(A2)
10 International Journal of Engineering Mathematics
Also
(119860119901119902 119861119901119902 119863119901119902)
=
119873
sum
119894=1
119862(119894)
119901119902
([119911119894+1
minus 119911119894] [
1199112
119894+1
minus 1199112
119894
2] [
1199113
119894+1
minus 1199113
119894
3])
(A3)
The coefficient matrices [119872] [119870] and [119871] appearing in(25) are given as
[119872] =[[
[
120575119878[11986366] 120575119878[11986326] 120575119878([11986136] minus [119861
45]119879
)
120575119878[11986326] [119863
22] [119861
23] minus [119861
44]119879
[0] [0] [11986344]
]]
]
[119870]=[
[
minus120575119878([11986055] + [120572]) minus120575
119878[11986045] [0]
minus120575119878[11986045] minus ([119860
44] + [120572]) [0]
120575119878([11986145]minus[11986136]119879
) [11986144]minus[11986123]119879
minus ([11986033]+[120572])
]
]
[119871] = [
[
12057511986011986055 0 0
12057511986011986045 0 0
minus120575119860(11986145 + 119861
36) 119860
13 12057511986211986113
]
]
(A4)
where [119860119901119902] [119861119901119902] and [119863
119901119902] are (119873 + 1) times (119873 + 1) square
matrices containing 119860119896119895119901119902 119861119896119895119901119902 and 119863
119896119895
119901119902 respectively and the
vectors 119860119901119902 119861119901119902 and 119861
119901119902 are (119873+1)times1 columnmatrices
containing 119860119896119901119902
119861119896119901119902
and 119861119896
119901119902
respectively Also [0] is (119873 +
1) times (119873 + 1) square zero and 0 is a zero vector with 119873 + 1
rows The artificial matrix [120572] is also an (119873 + 1) times (119873 + 1)
square matrix whose elements are given by
120572119896119895
= 120572int
ℎ2
minusℎ2
120601119896120601119895d119911 (A5)
with 120572 being a relatively small parameter in comparison withthe rigidity constants 119860119896119895
119901119902(119901119902 = 33 44 55) It is noted that
the insertion of [120572] in the matrix [119870] makes the eigenvaluesof the matrix (minus[119872]
minus1
[119870]) distinct
References
[1] T Kant and K Swaminathan ldquoEstimation of transverseinter-laminar stresses in laminated compositesmdasha selective reviewand survey of current developmentsrdquo Composite Structures vol49 no 1 pp 65ndash75 2000
[2] A H Puppo and H A Evensen ldquoInterlaminar shear ınlamınated composıtes under generalızed plane stressrdquo Journalof Composite Materials vol 4 pp 204ndash220 1970
[3] N J Pagano ldquoOn the calculatıon of ınterlamınar normal stressın composıte lamınaterdquo Journal of Composite Materials vol 8pp 65ndash81 1974
[4] P W Hsu and C T Herakovich ldquoEdge effects in angle-plycomposite laminatesrdquo Journal of CompositeMaterials vol 11 pp422ndash428 1977
[5] S Tang and A Levy ldquoBoundary layer theory 2 extension oflaminated finite striprdquo Journal of CompositeMaterials vol 9 no1 pp 42ndash52 1975
[6] R B Pipes andN J Pagano ldquoInterlaminar stresses in compositelaminates an approximate elasticity solutionrdquo Journal of AppliedMechanics vol 41 no 3 pp 668ndash672 1974
[7] N J Pagano ldquoStress fields in composite laminatesrdquo InternationalJournal of Solids and Structures vol 14 no 5 pp 385ndash400 1978
[8] S S Wang and I Choi ldquoBoundary-layer effects in composıtelaminates 1 free-edge stress singulaiıtiesrdquo Journal of AppliedMechanics vol V 49 no 3 pp 541ndash548 1982
[9] W L Yin ldquoFree-edge effects in anisotropic laminates underextension bending and twisting part I a stress-function-basedvariational approachrdquo Journal of Applied Mechanics vol 61 no2 pp 410ndash415 1994
[10] A S D Wang and F W Crossman ldquoSome new results on edgeeffect in symmetric composite laminatesrdquo Journal of CompositeMaterials vol 11 no 1 pp 92ndash106 1977
[11] J D Whitcomb I S Raju and J G Goree ldquoReliability ofthe finite element method for calculating free edge stresses incomposite laminatesrdquo Computers and Structures vol 15 no 1pp 23ndash37 1982
[12] G Davı ldquoStress fields in general composite laminatesrdquo AIAAJournal vol 34 no 12 pp 2604ndash2608 1996
[13] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT Part 1 derivationof finite element matricesrdquo International Journal for NumericalMethods in Engineering vol 55 no 2 pp 191ndash231 2002
[14] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT part 2 numericalimplementationsrdquo International Journal for Numerical Methodsin Engineering vol 55 no 3 pp 253ndash291 2002
[15] V-T Nguyen and J-F Caron ldquoFinite element analysis of free-edge stresses in composite laminates under mechanical anthermal loadingrdquo Composites Science and Technology vol 69no 1 pp 40ndash49 2009
[16] D H Robbins Jr and J N Reddy ldquoModelling of thick compos-ites using a layerwise laminate theoryrdquo International Journal forNumerical Methods in Engineering vol 36 no 4 pp 655ndash6771993
[17] C Mittelstedt and W Becker ldquoReddyrsquos layerwise laminate platetheory for the computation of elastic fields in the vicinity ofstraight free laminate edgesrdquoMaterials Science and EngineeringA vol 498 no 1-2 pp 76ndash80 2008
[18] W J Na Damage analysis of laminated composite beams underbending loads using the layer-wise theory [Dissertation thesis]Texas AampM University Texas Tex USA 2008
[19] T S Plagianakos and D A Saravanos ldquoHigher-order layerwiselaminate theory for the prediction of interlaminar shear stressesin thick composite and sandwich composite platesrdquo CompositeStructures vol 87 no 1 pp 23ndash35 2009
[20] H Ullah A R Harland T Lucas D Price and V V Sil-berschmidt ldquoFinite-element modelling of bending of CFRPlaminates multiple delaminationsrdquo Computational MaterialsScience vol 52 no 1 pp 147ndash156 2012
[21] F Helenon M R Wisnom S R Hallett and R S TraskldquoInvestigation into failure of laminated composite T-piecespecimens under bending loadingrdquo Composites A vol 54 pp182ndash189 2013
[22] C H Thai A J M Ferreira E Carrera and H Nguyen-XuanldquoIsogeometric analysis of laminated composite and sandwichplates using a layerwise deformation theoryrdquo Composite Struc-tures vol 104 pp 196ndash214 2013
International Journal of Engineering Mathematics 11
[23] N D Thai M DrsquoOttavio and J-F Caron ldquoBending analysis oflaminated and sandwich plates using a layer-wise stress modelrdquoComposite Structures vol 96 pp 135ndash142 2013
[24] PMalekzadeh ldquoA two-dimensional layerwise-differential quad-rature static analysis of thick laminated composite circulararchesrdquoAppliedMathematicalModelling vol 33 no 4 pp 1850ndash1861 2009
[25] Y C Fung and P Tong Classical and Computational SolidMechanics World Scientific New Jersey NJ USA 2001
[26] S G LekhnitskiiTheory of Elasticity of anAnisotropic BodyMirPublishers Moscow Russia 1981
[27] A Nosier R K Kapania and J N Reddy ldquoFree vibrationanalysis of laminated plates using a layerwise theoryrdquo AIAAJournal vol 31 no 12 pp 2335ndash2346 1993
[28] C T HerakovichMechanics of Fibrous Composites Wiley NewYork NY USA 1998
[29] O Goodsell and R B Pipes ldquoInterlaminar stresses in compositelaminates subjected to anticlastic bending deformationrdquo Journalof Applied Mechanics vol 80 no 4 pp 1ndash7 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
International Journal of Engineering Mathematics 9
exactly at the free edge (ie 119910 = 119887) Furthermore theinterlaminar normal stress 120590
119911grows rapidly in the vicinity of
the free edge while being zero in the interior region of thelaminate
5 Conclusions
In the present paper analytical solutions are developed toanalyze the interlaminar stresses for different lay-up con-figurations in laminated composite plates subjected to thebending moment The solutions were obtained based onthe reduced elasticity displacement field for long laminatedplates It is found that the components of the displacementsfield are composed of two distinct parts signifying theglobal and local deformations within laminates The localdisplacement functions as well as the interlaminar stressesthrough the layers of the laminate were found by Reddyrsquoslayerwise theory (LWT)Thenumerical results based onLWTwere shown for the free-edge interlaminar stresses throughthe thickness and across the interfaces of various cross-plysymmetric angle-ply and general composite laminates
Appendix
The laminate rigidities in (22a) (22b) (22c) (22d) (24a)(24b) and (24c) are defined as
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
1206011015840
119895
1206011198961206011015840
119895
120601119896120601119895) d119911
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
) =
119873
sum
119894=1
int
ℎ2
minusℎ2
119862(119894)
119901119902
(1206011015840
119896
120601119896 1206011015840
119896
119911 120601119896119911) d119911
(119896 119895 = 1 2 119873 + 1)
(119860119901119902 119861119901119902 119863119901119902) =
119873
sum
119894=1
int
119911119894+1
119911119894
119862(119894)
119901119902
(1 119911 1199112
) d119911
(A1)
which upon integration are presented in the following form
(119860119896119895
119901119902
119861119896119895
119901119902
119863119896119895
119901119902
)
=
(minus
119862(119896minus1)
119901119902
ℎ119896minus1
minus
119862(119896minus1)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
6) if 119895 = 119896 minus 1
(
119862(119896minus1)
119901119902
ℎ119896minus1
+
119862(119896)
119901119902
ℎ119896
119862(119896minus1)
119901119902
2minus
119862(119896)
119901119902
2
ℎ119896minus1
119862(119896minus1)
119901119902
3+
ℎ119896119862(119896)
119901119902
3) if 119895 = 119896
(minus
119862(119896)
119901119902
ℎ119896
119862(119896)
119901119902
2
ℎ119896119862(119896)
119901119902
6) if 119895 = 119896 + 1
(0 0 0) if 119895 lt 119896 minus 1 or 119895 gt 119896 + 1
(119860119896
119901119902
119861119896
119901119902
119861119896
119901119902
119863119896
119901119902
)
=
(minus119862(1)
119901119902
ℎ1119862(1)
119901119902
2 119862(1)
119901119902
1199112
1
minus 1199112
2
2ℎ1
119862(1)
119901119902
ℎ1
[1199113
1
minus 1199113
2
3minus 1199112
1199112
1
minus 1199112
2
2]) if 119896 = 1
(minus119862(119896minus1)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2]) if 119896 = 119873 + 1
(119862(119896minus1)
119901119902
minus 119862(119896)
119901119902
ℎ119896minus1
119862(119896minus1)
119901119902
2+
ℎ119896119862(119896)
119901119902
2 119862(119896minus1)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896minus1
+ 119862(119896)
119901119902
1199112
119896
minus 1199112
119896minus1
2ℎ119896
119862(119896minus1)
119901119902
ℎ119896minus1
[1199113
119896
minus 1199113
119896minus1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896minus1
2] +
119862(119896)
119901119902
ℎ119896
[1199113
119896
minus 1199113
119896+1
3minus 119911119896minus1
1199112
119896
minus 1199112
119896+1
2]) if 1 lt 119896 lt 119873 + 1
(A2)
10 International Journal of Engineering Mathematics
Also
(119860119901119902 119861119901119902 119863119901119902)
=
119873
sum
119894=1
119862(119894)
119901119902
([119911119894+1
minus 119911119894] [
1199112
119894+1
minus 1199112
119894
2] [
1199113
119894+1
minus 1199113
119894
3])
(A3)
The coefficient matrices [119872] [119870] and [119871] appearing in(25) are given as
[119872] =[[
[
120575119878[11986366] 120575119878[11986326] 120575119878([11986136] minus [119861
45]119879
)
120575119878[11986326] [119863
22] [119861
23] minus [119861
44]119879
[0] [0] [11986344]
]]
]
[119870]=[
[
minus120575119878([11986055] + [120572]) minus120575
119878[11986045] [0]
minus120575119878[11986045] minus ([119860
44] + [120572]) [0]
120575119878([11986145]minus[11986136]119879
) [11986144]minus[11986123]119879
minus ([11986033]+[120572])
]
]
[119871] = [
[
12057511986011986055 0 0
12057511986011986045 0 0
minus120575119860(11986145 + 119861
36) 119860
13 12057511986211986113
]
]
(A4)
where [119860119901119902] [119861119901119902] and [119863
119901119902] are (119873 + 1) times (119873 + 1) square
matrices containing 119860119896119895119901119902 119861119896119895119901119902 and 119863
119896119895
119901119902 respectively and the
vectors 119860119901119902 119861119901119902 and 119861
119901119902 are (119873+1)times1 columnmatrices
containing 119860119896119901119902
119861119896119901119902
and 119861119896
119901119902
respectively Also [0] is (119873 +
1) times (119873 + 1) square zero and 0 is a zero vector with 119873 + 1
rows The artificial matrix [120572] is also an (119873 + 1) times (119873 + 1)
square matrix whose elements are given by
120572119896119895
= 120572int
ℎ2
minusℎ2
120601119896120601119895d119911 (A5)
with 120572 being a relatively small parameter in comparison withthe rigidity constants 119860119896119895
119901119902(119901119902 = 33 44 55) It is noted that
the insertion of [120572] in the matrix [119870] makes the eigenvaluesof the matrix (minus[119872]
minus1
[119870]) distinct
References
[1] T Kant and K Swaminathan ldquoEstimation of transverseinter-laminar stresses in laminated compositesmdasha selective reviewand survey of current developmentsrdquo Composite Structures vol49 no 1 pp 65ndash75 2000
[2] A H Puppo and H A Evensen ldquoInterlaminar shear ınlamınated composıtes under generalızed plane stressrdquo Journalof Composite Materials vol 4 pp 204ndash220 1970
[3] N J Pagano ldquoOn the calculatıon of ınterlamınar normal stressın composıte lamınaterdquo Journal of Composite Materials vol 8pp 65ndash81 1974
[4] P W Hsu and C T Herakovich ldquoEdge effects in angle-plycomposite laminatesrdquo Journal of CompositeMaterials vol 11 pp422ndash428 1977
[5] S Tang and A Levy ldquoBoundary layer theory 2 extension oflaminated finite striprdquo Journal of CompositeMaterials vol 9 no1 pp 42ndash52 1975
[6] R B Pipes andN J Pagano ldquoInterlaminar stresses in compositelaminates an approximate elasticity solutionrdquo Journal of AppliedMechanics vol 41 no 3 pp 668ndash672 1974
[7] N J Pagano ldquoStress fields in composite laminatesrdquo InternationalJournal of Solids and Structures vol 14 no 5 pp 385ndash400 1978
[8] S S Wang and I Choi ldquoBoundary-layer effects in composıtelaminates 1 free-edge stress singulaiıtiesrdquo Journal of AppliedMechanics vol V 49 no 3 pp 541ndash548 1982
[9] W L Yin ldquoFree-edge effects in anisotropic laminates underextension bending and twisting part I a stress-function-basedvariational approachrdquo Journal of Applied Mechanics vol 61 no2 pp 410ndash415 1994
[10] A S D Wang and F W Crossman ldquoSome new results on edgeeffect in symmetric composite laminatesrdquo Journal of CompositeMaterials vol 11 no 1 pp 92ndash106 1977
[11] J D Whitcomb I S Raju and J G Goree ldquoReliability ofthe finite element method for calculating free edge stresses incomposite laminatesrdquo Computers and Structures vol 15 no 1pp 23ndash37 1982
[12] G Davı ldquoStress fields in general composite laminatesrdquo AIAAJournal vol 34 no 12 pp 2604ndash2608 1996
[13] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT Part 1 derivationof finite element matricesrdquo International Journal for NumericalMethods in Engineering vol 55 no 2 pp 191ndash231 2002
[14] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT part 2 numericalimplementationsrdquo International Journal for Numerical Methodsin Engineering vol 55 no 3 pp 253ndash291 2002
[15] V-T Nguyen and J-F Caron ldquoFinite element analysis of free-edge stresses in composite laminates under mechanical anthermal loadingrdquo Composites Science and Technology vol 69no 1 pp 40ndash49 2009
[16] D H Robbins Jr and J N Reddy ldquoModelling of thick compos-ites using a layerwise laminate theoryrdquo International Journal forNumerical Methods in Engineering vol 36 no 4 pp 655ndash6771993
[17] C Mittelstedt and W Becker ldquoReddyrsquos layerwise laminate platetheory for the computation of elastic fields in the vicinity ofstraight free laminate edgesrdquoMaterials Science and EngineeringA vol 498 no 1-2 pp 76ndash80 2008
[18] W J Na Damage analysis of laminated composite beams underbending loads using the layer-wise theory [Dissertation thesis]Texas AampM University Texas Tex USA 2008
[19] T S Plagianakos and D A Saravanos ldquoHigher-order layerwiselaminate theory for the prediction of interlaminar shear stressesin thick composite and sandwich composite platesrdquo CompositeStructures vol 87 no 1 pp 23ndash35 2009
[20] H Ullah A R Harland T Lucas D Price and V V Sil-berschmidt ldquoFinite-element modelling of bending of CFRPlaminates multiple delaminationsrdquo Computational MaterialsScience vol 52 no 1 pp 147ndash156 2012
[21] F Helenon M R Wisnom S R Hallett and R S TraskldquoInvestigation into failure of laminated composite T-piecespecimens under bending loadingrdquo Composites A vol 54 pp182ndash189 2013
[22] C H Thai A J M Ferreira E Carrera and H Nguyen-XuanldquoIsogeometric analysis of laminated composite and sandwichplates using a layerwise deformation theoryrdquo Composite Struc-tures vol 104 pp 196ndash214 2013
International Journal of Engineering Mathematics 11
[23] N D Thai M DrsquoOttavio and J-F Caron ldquoBending analysis oflaminated and sandwich plates using a layer-wise stress modelrdquoComposite Structures vol 96 pp 135ndash142 2013
[24] PMalekzadeh ldquoA two-dimensional layerwise-differential quad-rature static analysis of thick laminated composite circulararchesrdquoAppliedMathematicalModelling vol 33 no 4 pp 1850ndash1861 2009
[25] Y C Fung and P Tong Classical and Computational SolidMechanics World Scientific New Jersey NJ USA 2001
[26] S G LekhnitskiiTheory of Elasticity of anAnisotropic BodyMirPublishers Moscow Russia 1981
[27] A Nosier R K Kapania and J N Reddy ldquoFree vibrationanalysis of laminated plates using a layerwise theoryrdquo AIAAJournal vol 31 no 12 pp 2335ndash2346 1993
[28] C T HerakovichMechanics of Fibrous Composites Wiley NewYork NY USA 1998
[29] O Goodsell and R B Pipes ldquoInterlaminar stresses in compositelaminates subjected to anticlastic bending deformationrdquo Journalof Applied Mechanics vol 80 no 4 pp 1ndash7 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
10 International Journal of Engineering Mathematics
Also
(119860119901119902 119861119901119902 119863119901119902)
=
119873
sum
119894=1
119862(119894)
119901119902
([119911119894+1
minus 119911119894] [
1199112
119894+1
minus 1199112
119894
2] [
1199113
119894+1
minus 1199113
119894
3])
(A3)
The coefficient matrices [119872] [119870] and [119871] appearing in(25) are given as
[119872] =[[
[
120575119878[11986366] 120575119878[11986326] 120575119878([11986136] minus [119861
45]119879
)
120575119878[11986326] [119863
22] [119861
23] minus [119861
44]119879
[0] [0] [11986344]
]]
]
[119870]=[
[
minus120575119878([11986055] + [120572]) minus120575
119878[11986045] [0]
minus120575119878[11986045] minus ([119860
44] + [120572]) [0]
120575119878([11986145]minus[11986136]119879
) [11986144]minus[11986123]119879
minus ([11986033]+[120572])
]
]
[119871] = [
[
12057511986011986055 0 0
12057511986011986045 0 0
minus120575119860(11986145 + 119861
36) 119860
13 12057511986211986113
]
]
(A4)
where [119860119901119902] [119861119901119902] and [119863
119901119902] are (119873 + 1) times (119873 + 1) square
matrices containing 119860119896119895119901119902 119861119896119895119901119902 and 119863
119896119895
119901119902 respectively and the
vectors 119860119901119902 119861119901119902 and 119861
119901119902 are (119873+1)times1 columnmatrices
containing 119860119896119901119902
119861119896119901119902
and 119861119896
119901119902
respectively Also [0] is (119873 +
1) times (119873 + 1) square zero and 0 is a zero vector with 119873 + 1
rows The artificial matrix [120572] is also an (119873 + 1) times (119873 + 1)
square matrix whose elements are given by
120572119896119895
= 120572int
ℎ2
minusℎ2
120601119896120601119895d119911 (A5)
with 120572 being a relatively small parameter in comparison withthe rigidity constants 119860119896119895
119901119902(119901119902 = 33 44 55) It is noted that
the insertion of [120572] in the matrix [119870] makes the eigenvaluesof the matrix (minus[119872]
minus1
[119870]) distinct
References
[1] T Kant and K Swaminathan ldquoEstimation of transverseinter-laminar stresses in laminated compositesmdasha selective reviewand survey of current developmentsrdquo Composite Structures vol49 no 1 pp 65ndash75 2000
[2] A H Puppo and H A Evensen ldquoInterlaminar shear ınlamınated composıtes under generalızed plane stressrdquo Journalof Composite Materials vol 4 pp 204ndash220 1970
[3] N J Pagano ldquoOn the calculatıon of ınterlamınar normal stressın composıte lamınaterdquo Journal of Composite Materials vol 8pp 65ndash81 1974
[4] P W Hsu and C T Herakovich ldquoEdge effects in angle-plycomposite laminatesrdquo Journal of CompositeMaterials vol 11 pp422ndash428 1977
[5] S Tang and A Levy ldquoBoundary layer theory 2 extension oflaminated finite striprdquo Journal of CompositeMaterials vol 9 no1 pp 42ndash52 1975
[6] R B Pipes andN J Pagano ldquoInterlaminar stresses in compositelaminates an approximate elasticity solutionrdquo Journal of AppliedMechanics vol 41 no 3 pp 668ndash672 1974
[7] N J Pagano ldquoStress fields in composite laminatesrdquo InternationalJournal of Solids and Structures vol 14 no 5 pp 385ndash400 1978
[8] S S Wang and I Choi ldquoBoundary-layer effects in composıtelaminates 1 free-edge stress singulaiıtiesrdquo Journal of AppliedMechanics vol V 49 no 3 pp 541ndash548 1982
[9] W L Yin ldquoFree-edge effects in anisotropic laminates underextension bending and twisting part I a stress-function-basedvariational approachrdquo Journal of Applied Mechanics vol 61 no2 pp 410ndash415 1994
[10] A S D Wang and F W Crossman ldquoSome new results on edgeeffect in symmetric composite laminatesrdquo Journal of CompositeMaterials vol 11 no 1 pp 92ndash106 1977
[11] J D Whitcomb I S Raju and J G Goree ldquoReliability ofthe finite element method for calculating free edge stresses incomposite laminatesrdquo Computers and Structures vol 15 no 1pp 23ndash37 1982
[12] G Davı ldquoStress fields in general composite laminatesrdquo AIAAJournal vol 34 no 12 pp 2604ndash2608 1996
[13] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT Part 1 derivationof finite element matricesrdquo International Journal for NumericalMethods in Engineering vol 55 no 2 pp 191ndash231 2002
[14] E Carrera and L Demasi ldquoClassical and advancedmultilayeredplate elements based upon PVD and RMVT part 2 numericalimplementationsrdquo International Journal for Numerical Methodsin Engineering vol 55 no 3 pp 253ndash291 2002
[15] V-T Nguyen and J-F Caron ldquoFinite element analysis of free-edge stresses in composite laminates under mechanical anthermal loadingrdquo Composites Science and Technology vol 69no 1 pp 40ndash49 2009
[16] D H Robbins Jr and J N Reddy ldquoModelling of thick compos-ites using a layerwise laminate theoryrdquo International Journal forNumerical Methods in Engineering vol 36 no 4 pp 655ndash6771993
[17] C Mittelstedt and W Becker ldquoReddyrsquos layerwise laminate platetheory for the computation of elastic fields in the vicinity ofstraight free laminate edgesrdquoMaterials Science and EngineeringA vol 498 no 1-2 pp 76ndash80 2008
[18] W J Na Damage analysis of laminated composite beams underbending loads using the layer-wise theory [Dissertation thesis]Texas AampM University Texas Tex USA 2008
[19] T S Plagianakos and D A Saravanos ldquoHigher-order layerwiselaminate theory for the prediction of interlaminar shear stressesin thick composite and sandwich composite platesrdquo CompositeStructures vol 87 no 1 pp 23ndash35 2009
[20] H Ullah A R Harland T Lucas D Price and V V Sil-berschmidt ldquoFinite-element modelling of bending of CFRPlaminates multiple delaminationsrdquo Computational MaterialsScience vol 52 no 1 pp 147ndash156 2012
[21] F Helenon M R Wisnom S R Hallett and R S TraskldquoInvestigation into failure of laminated composite T-piecespecimens under bending loadingrdquo Composites A vol 54 pp182ndash189 2013
[22] C H Thai A J M Ferreira E Carrera and H Nguyen-XuanldquoIsogeometric analysis of laminated composite and sandwichplates using a layerwise deformation theoryrdquo Composite Struc-tures vol 104 pp 196ndash214 2013
International Journal of Engineering Mathematics 11
[23] N D Thai M DrsquoOttavio and J-F Caron ldquoBending analysis oflaminated and sandwich plates using a layer-wise stress modelrdquoComposite Structures vol 96 pp 135ndash142 2013
[24] PMalekzadeh ldquoA two-dimensional layerwise-differential quad-rature static analysis of thick laminated composite circulararchesrdquoAppliedMathematicalModelling vol 33 no 4 pp 1850ndash1861 2009
[25] Y C Fung and P Tong Classical and Computational SolidMechanics World Scientific New Jersey NJ USA 2001
[26] S G LekhnitskiiTheory of Elasticity of anAnisotropic BodyMirPublishers Moscow Russia 1981
[27] A Nosier R K Kapania and J N Reddy ldquoFree vibrationanalysis of laminated plates using a layerwise theoryrdquo AIAAJournal vol 31 no 12 pp 2335ndash2346 1993
[28] C T HerakovichMechanics of Fibrous Composites Wiley NewYork NY USA 1998
[29] O Goodsell and R B Pipes ldquoInterlaminar stresses in compositelaminates subjected to anticlastic bending deformationrdquo Journalof Applied Mechanics vol 80 no 4 pp 1ndash7 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
International Journal of Engineering Mathematics 11
[23] N D Thai M DrsquoOttavio and J-F Caron ldquoBending analysis oflaminated and sandwich plates using a layer-wise stress modelrdquoComposite Structures vol 96 pp 135ndash142 2013
[24] PMalekzadeh ldquoA two-dimensional layerwise-differential quad-rature static analysis of thick laminated composite circulararchesrdquoAppliedMathematicalModelling vol 33 no 4 pp 1850ndash1861 2009
[25] Y C Fung and P Tong Classical and Computational SolidMechanics World Scientific New Jersey NJ USA 2001
[26] S G LekhnitskiiTheory of Elasticity of anAnisotropic BodyMirPublishers Moscow Russia 1981
[27] A Nosier R K Kapania and J N Reddy ldquoFree vibrationanalysis of laminated plates using a layerwise theoryrdquo AIAAJournal vol 31 no 12 pp 2335ndash2346 1993
[28] C T HerakovichMechanics of Fibrous Composites Wiley NewYork NY USA 1998
[29] O Goodsell and R B Pipes ldquoInterlaminar stresses in compositelaminates subjected to anticlastic bending deformationrdquo Journalof Applied Mechanics vol 80 no 4 pp 1ndash7 2013
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical Problems in Engineering
Hindawi Publishing Corporationhttpwwwhindawicom
Differential EquationsInternational Journal of
Volume 2014
Applied MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Probability and StatisticsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mathematical PhysicsAdvances in
Complex AnalysisJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
OptimizationJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CombinatoricsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Operations ResearchAdvances in
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Function Spaces
Abstract and Applied AnalysisHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of Mathematics and Mathematical Sciences
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Algebra
Discrete Dynamics in Nature and Society
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Decision SciencesAdvances in
Discrete MathematicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
Volume 2014 Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Stochastic AnalysisInternational Journal of