Project Fall 2012

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AE 569 - FALL 2012 PROJECT FOR GRADUATE STUDENTS

(due January 26th Saturday- if not finished by Jan. 26, you can use incomplete time till

February 2 nd 2013)

FINITE ELEMENT ANALYSIS BASED PROGRESSIVE FAILURE ANALYSIS OF

LAMINATED COMPOSITE STRUCTURES

1. INTRODUCTION AND GENERAL DESCRIPTION OF THE FINITE ELEMENT

BASED PROGRESSIVE FAILURE ANALYSIS

In this project groups (2 student per group) are expected to perform progressive failureanalysis of a composite laminate with a central hole by finite element analysis. Students areexpected to use a commercial finite element program as a solver, and write a code which will

perform failure analysis and progress failure by employing sudden material propertydegradation using load controlled numerical test. Students should not use the progressivefailure analysis modules of certain commercial codes such as Abaqus, MSC Nastran 2012 etc.The idea is to write a progressive failure analysis code and employ a commercial finite

element code as a solver. This way, failure analysis code can be expanded by employingdifferent failure theories.

Two flowcharts of the progressive failure analysis were discussed in class. Flowcharts arelinked in the course web site. These flowcharts are specific for hand calculation. In this

project, finite element based progressive failure analysis will be performed by editing theinput file of the finite element code which includes all the model information. This process issummarized below in Fig.1.

Fig. 1 Simplified flowchart of finite element analysis based progressive failure analysis

Prepare theFE modeland input

file(includingthe load

Carry out FEsolution anddetermine

layerstresses/strains.FE code has toexecutedexternally fromthe main codethat you willwrite

Read the output file ofthe FE code(specifically read layer

stresses and strainsdepending the on thefailure criterion used

Determine thefailure indicesinside your code

(of the particularfailure criterion)

Check if any plyfails or not

If no failure of any plyis predicted, incrementthe load by editing the

input file of the FEcode.

If failure of any ply is predicted,employ the material propertydegradation scheme and degradethe material property of the plymaterial. This will be done byediting the input file. Do notincrement load.

Check ultimatefailure and stopaccordingly orstop when a

particular loadlevel is reached.


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NOTE: Students who find it hard to fully automate the failure progression, via an externalcode, which does everything (runs FE code, reads output file, calculates failure indices basedon the failure criterion used, performs material property degradation and modifes the inputfile), can have a separate code calculating failure indices and execute FE runs separately.This way, the process will not be automatic, and the user has to intervene at every step of the

failure progression.

In order to effectively allow material property degradation at the ply level, for eachelement in the finite element mesh distinct composite laminate properties with distinct twodimensional orthotropic materials has to be generated. Stiffness reduction scheme can then beimplemented easily for the failed ply by referencing the element property identification andmaterial identification numbers of the ply.

A typical input file (.bdf) of Nastran is shown below. In this file PCOMP refers to thecomposite property identification cards. In order to progress failure at the ply level, distinctcomposite property identification has to be assigned for each element. These are given by thered numbers in the PCOMP cards. The blue numbers in the PCOMP cards refer to the layer

materials. Thus, for each layer we define a new material. CQUAD4 cards refer to elements.The green numbers, in the CQUAD4 cards, refer to the element numbers and the red numbersin the CQUAD4 cards refer to the composite property cards PCOMP. MAT8 cards define the2D orthotropic materials. Thus, in the example .bdf file given below, we have N*L number oflayer materials defined (L: # of layers in an element, N: # of elements in the model). Duringmaterial property degradation, all we have to identify is the number of the MAT8 cards thatwe should modify depending on whether failure is predicted or not. Once the related MAT8card is modified, composite properties (PCOMP cards) will be automatically updated sincePCOMP cards reference material MAT8 cards, as indicated by the blue numbers shown in thePCOMP cards. (Note that for ease of explanation, this input file is edited and brought into theform shown below)

An example output file is given after the input file. In this example, it is assumed thatlaminate has two plies. After the output file is created (following a Nastran run), the linesgiving the stress results should be read. While reading the lines, element IDs and ply IDsshould also be read and recorded. If failure of any particular layer is predicted, element IDand ply ID will be used to find the ID number of the MAT8 cards. Once the IDs of the failed

plies are identified, these MAT8 cards should be modified in the input file. After themodification of the MAT8 cards, the code has to call for another FE run and the whole

process will start all over again.

NOTE: Students who want to use other FE codes such as Abaqus, Ansys can do so. In that

case, they have to use the input and output files of those programs, and carry out the readingand editing operations accordingly.

The main code that will perform progessive failure analysis can be written in FORTRAN,PYTHON, PERL (Ansys uses this script language), MATLAB, VISUAL BASIC etc.Remember that you have to read and edit text files many times during the progressive failureanalysis. Therefore, you should use the code that you are most comfortable with.


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-----------------------------------------------------------------------------------------------------------------EXAMPLE INPUT FILE OF NASTRAN

RED: PCOMP PROPERTY NUMBERS-PCOMP NO.BLUE: LAYER MATERIAL NUMBERS - MID MO. and MAT8 numbersGREEN: ELEMENT NUMBERS - CQUAD4 NO.

$ NASTRAN input file created by the MSC MSC.Nastran input file$ translator ( MSC.Patran 13.1.116 ) on October 24, 2009 at 11:13:35.$$ Direct Text Input for Bulk Data$ Elements and Element Properties for region : shell$ Composite Property Record created from P3/PATRAN composite material$ record : lam$ Composite Material Description :PCOMP 1 50. TSAI 0. 0. 1 .25 0. YES

2 .25 10. YES 3 .25 20. YES

. . . . .

. . . . .

. . . . .

L .25 20. YESPCOMP 2 50. TSAI 0. 0. L+1 .25 0. YES

L+2 .25 10. YES L+3 .25 20. YES

. . . . .

. . . . .

2L .25 20. YES. . . . .

. . . . .

PCOMP N 50. TSAI 0. 0. (N-1)L+1 .25 0. YES

(N-1)L+2 .25 20. YES

NL .25 40. YES 1 .25 50. YES$

$CQUAD4 1 1 1 2 11 10 0.CQUAD4 2 2 2 3 12 11 0.CQUAD4 3 3 3 4 13 12 0.. . . . . . . . .

. . . . . . . . .

. . . . . . . . .

CQUAD4 N N 71 72 81 80 0.

$ Referenced Material Records

$ Material Record : ortho$ Description of Material : Date: 27-Dec-08 Time: 16:36:32


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MAT8 1 181000. 10300. .28 7170. 7170. 5000. 1.6-91500. 1500. 40. 246. 68.

-.5MAT8 2 181000. 10300. .28 7170. 7170. 5000. 1.6-9

1500. 1500. 40. 246. 68.

-.5MAT8 3 181000. 10300. .28 7170. 7170. 5000. 1.6-9

1500. 1500. 40. 246. 68.-.5

. . . . . . . . .

. . . . . . . . .

MAT8 N*L 181000. 10300. .28 7170. 7170. 5000. 1.6-91500. 1500. 40. 246. 68.

-.5$ Nodes of the Entire ModelGRID 1 0. 0. 0.

GRID 2 125. 0. 0.GRID 3 250. 0. 0.GRID 4 375. 0. 0.GRID 5 500. 0. 0.GRID 6 625. 0. 0.GRID 7 750. 0. 0.GRID 8 875. 0. 0.GRID 9 1000. 0. 0.GRID 10 0. 125. 0.GRID 11 125. 125. 0.GRID 12 250. 125. 0.GRID 13 375. 125. 0.GRID 14 500. 125. 0.GRID 15 625. 125. 0.GRID 16 750. 125. 0.$ Loads for Load Case : Default$ Displacement Constraints of Load Set : nSPC1 1 123 1 THRU 9$ Displacement Constraints of Load Set : n1SPC1 3 3 73$ Pressure Loads of Load Set : p

PLOAD4 1 1 -1.-4 THRU 64-----------------------------------------------------------------------------------------------------------------EXAMPLE OUTPUT FILE OF NASTRAN

ELEMENT PLY STRESSES IN FIBER AND MATRIX DIRECTIONS

ID ID NORMAL-1 NORMAL-2 SHEAR-12

1 1 3.00725E+04 -4.84032E+03 4.64574E+03

1 2 8.26329E+04 7.01767E+02 -8.22791E+03

2 1 3.85178E+04 -1.02513E+04 3.31139E+03

2 2 4.51463E+04 -5.88696E+02 -1.19184E+04

3 1 4.05495E+04 -1.06741E+04 2.74296E+03

3 2 4.54650E+04 -6.57785E+02 -1.21436E+04

. . . . .

. . . . .

---------------------------------------------------------------------------


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2. MODEL DESCRIPTION

The model which will be used in the progressive failure analysis is a square compositelaminate with a central hole shown in Fig. 2 below. The material properties of the ply material(fiber: T300/matrix: F934) is given by:

E1=148 GPa, E2=9.65 GPa, v12=0.3, G=4.55 GPaXt=1314 MPa, Xc=1220 MPa, Yt=43 MPa, Yc=168 MPa, S=48 MPa

Ply thickness: 0.10 mm

Laminate configurations to be investigated: [0/0], [90/90] , [0/90] and [-45/45]

NOTE: In order to make a simple model, in this project only two plies per element are usedin the laminate.

Fig. 2 Squarecomposite laminate with a central hole

Laminates with the central holes will be investigated under uniaxial loading as shown in Fig.3. Model the uniformly distributed load using CID distributed load option. Section of theinput file which gives the nodal forces for a sample distributed load case is given below. In

this example a uniformly distributed load of 10 N/m is distributed along an edge which has alength of 0.05m. On the edge there are 3 elements (same length) and four nodes. The cornernodes 14 and 56 take a share of (10*(0.05/3))/2=0.08333 N. The middle nodes 28 and 42 takeup 2*(10*(0.05/3))/2=0.16667 N. So, while increasing the loads you need to change the fieldswhich gives the nodal loads which are 0.08333 N in this example.

FORCE 1 14 .08333331. 0. 0.FORCE 1 28 .08333331. 0. 0.FORCE 1 28 .08333331. 0. 0.FORCE 1 42 .08333331. 0. 0.FORCE 1 42 .08333331. 0. 0.

FORCE 1 56 .08333331. 0. 0.

10 cm

Hole diameter = 3 cmx, 0o

y, 90o


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Fig. 3 Uniaxial tensile loading

During the finite element analysis, due to symmetry only quarter laminate will be modeled.The model is shown in Fig. 4 for the uniaxial tensile loading. Finite element model has 36elements and 2 plies per element. Thus, total number of 2D orthotropic materials to bedefined, is 72.

It is assumed that the tests are carried on a uniaxial test machine. Therefore, boundaryconditions are defined accordingly.1: x disp. , 2: y disp. , 3: z displ. , 4: x-axis rot. , 5: y-axis rot. , 6: z-axis rot.

In the project, you are also asked to draw the load displacement curve. For the displacement,you can take the x-displacement of the corner node shown in Fig. 4 to draw the loaddisplacement curve. To draw the load displacement curve, at each step you need to store thevalue of the distributed load and displacement of the corner node. In some steps load will besame but due to failure of plies, because of material propety degradation, displacement willchange. Therefore, to get the full picture of load-displacement history, you need to store theload and displacement values at every step.

Fig. 4 Finite element model for the uniaxial tensile loading

Nx (N/m)

3=01=5=0

2=4=0

Nx (N/m)

Use the displacement ofthis node to draw the loaddisplacementcurve


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3. FAILURE CRITERIA AND MATERIAL PROPERTY DEGRADATION METHOD

Failure Criteria

Two dimensional Tsai-Wu failure criteria will be implemented in the progressive failureanalysis code.

References:

Tsai-WuS.W. Tsai, A General theory of strength for anisotropic materials, Journal ofComposite Materials, 5(1), 58-80 (1971).

Material Property Degradation

Use sudden degradation and a stiffness reduction factor of 0.001. Once failure is predicted,degrade all properties at once. This is the so-called complete ply failure method which is theconservative approach. Degrade E1,E2,G12,G13,G23,v12 by the reduction factor of 0.001.Once a property is degraded, make sure that you do not degrade it again during failure

progression or load increase.

4. PROJECT REQUIREMENTS

a) For the uniaxial tensile load case, students are expected to determine first ply load,failure progression and ultimate failure load. For failure progression prepare simple

plots at intermediate load steps (not all load steps) such as shown below.

Load level: Nx = XXX

where the green dot shows that a single layer has failed in that element and red dot showsthat both layers have failed.


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NOTE: For ultimate failure, all layers of the elements in the FE model along a line must befailed. So, you should have all red dots along a line which breaks the laminate into two suchas the one shown in the figure below.

b) Report first ply and ultimate loads for the four different laminate configurations intabular form. Comment on the first ply and ultimate failure loads of the fourlaminates studied.

Also for the four different laminates, plot load versus displacement curve. Load anddisplacement definitions are made in the previous section.

c) Write an project report which has the following sub-sections:

- Title page, group members- Introduction: Give a brief introduction- Description of your code (or your methodology)- Verification of your code (present a verification for the no hole case. And

compare first ply load with the hand calculation (such as the one done in class)- Results: response to project requirements should be given here.- Conclusion : Make concluding remarks.- Appendix: Give the main code you have written, initial input file of the FE

code, and initial (after first run) output file of the FE code

HOW TO CALL FOR NASTRAN RUN FROM YOUR CODE

FORTRAN USERS:Students who use Fortran can use the following statements to call Nastran runs inside theFortran code.

CALL SYSTEM('C:\MSC.Software\MSC.Nastran\bin\mdnast2008.exe agard.bdf')

Note that you have to address the folder where the nastran.exe file resides. The following isanother example. For instance, if your nastran.exe is under D drive then address that.


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CALLSYSTEM('D:\Users\ERKUT\AppData\Roaming\MSC.Software\MD_Nastran\bin\mdnast2008.exe agard.bdf')

Important Note: There are two .exe files for Nastran. One ends with w and one does nothave w.

Do not use mdnast2008w.exe or nastranw.exe (exe files with w ).

In that case Fortran code does not waitfor the nastran run to complete its execution.

Use mdnast2008.exe or nastran.exe.

In that case Fortran code waits for the nastran run to complete its execution.

MATLAB USERS:

You may use the following command. Again use .exe file which does not end with w.

system ('C:\MSC.Software\MSC.Nastran\bin\mdnast2008.exe agard.bdf')

Project Fall 2012

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