Aircraft Structures Lab II Manual for AUC R2008_S

8/10/2019 Aircraft Structures Lab II Manual for AUC R2008_S

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DHANALAKSHMI SRINIVASAN ENGINEERING COLLEGE

(Approved by AICTE, New Delhi & Affiliated to Anna University, Chennai 600 025)

(NBA Accredited and ISO 9001:2008 Certified Institution)PERAMBALUR - 621 212.

DEPARTMENT OF AERONAUTICAL ENGINEERING

AE 2305 Aircraft Structures Laboratory II

MANUAL NOTE BOOK

Name : .

Reg. No. : .

Semester : .

Academic Year : .


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Dhanalakshmi Srinivasan Engineering College, Perambalur 621 212. AUC R2008

Gurunath K |V Semester [2014 2015]

AE2305 AIRCRAFT STRUCTURES LAB II L T P C0 0 3 2

OBJECTIVETo experimentally study the unsymmetrical bending of beams, find the location of shearcentre, obtain the stresses in circular discs and beams using photoelastic techniques,calibration of photo elastic materials and study on vibration of beams.

LIST OF EXPERIMENTS

1. Unsymmetrical bending of Z-section beams2. Shear centre location for open channel sections3. Shear centre location for closed D-sections4. Constant strength beam5. Flexibility matrix for cantilever beam6. Beam with combined loading

7. Calibration of Photo- elastic materials8. Stresses in circular discs and beams using photo elastic techniques9. Determination of natural frequencies of cantilever beams10. Wagner beam Tension field beam

TOTAL: 45 PERIODS

LIST OF EQUIPMENT(for a batch of 30 students)

Sl. No. Name of the Equipment Qty Experiments Number

1 Beam Test set up 2 1, 2, 3,4, 52 Unsymmetrical Z section beam 1 1

3 Channel section beam 1 2

4 Closed D section beam 1 3

5 Dial gauges 12 1,2,3

6 Strain indicator and strain gauges One set 4,5,6

7 Photo elastic apparatus 1 7,8

8 Amplifier 2 9

9 Exciter 2 9

10 Pick up 2 9

11 Oscilloscope 2 9

12 Wagner beam 1 10

13 Hydraulic Jack 1 10


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CONTENTS

Sl. No. Date Name of the Experiment Page Marks Sign


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Completed / Not Completed

Signature of Staff in Charge

AverageMarks


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Gurunath K AE 2305 Aircraft Structures Laboratory II | 1

Aircraft Structures Laboratory II

List of Experiments

1. Unsymmetrical Bending of Beams.

2. Shear Centre Location for Open Sections.

3. Shear Centre Location for Closed Sections.

4. Constant Strength Beam.

5. Beam with Combined Loading.

6. Structural Behaviour of a Semi-Tension Field Beam (Wagner Beam).

7. Determination of Natural Frequencies of Cantilever Beams.

8. Stresses in Circular Discs using Photo elastic Techniques


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Extension Piece

Wa Wa

W H

2Wa = W V

Determination of Principal axes

Shear center


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AIM:To determine the principal axes of an unsymmetrical section.

THEORY:

The well-known flexure formula = based on the elementary theory of bendingof beams assumes that the load is always applied through one of the principal axes of thesection. Actually, even if the applied load passes through the centroid and/or the shear centreof the section, the plane of bending and the plane of loading need not necessarily are the same.Therefore, a knowledge of the location of the principal axes is required for the determination

of the stress distribution in beams (of any arbitrary cross section) using flexure formula. Thedetermination of the principal axes experimentally is described here.

If I x, Iy and I xy are the moments and product of inertia of any section about an arbitraryorthogonal centroidal axes OX and OY then the inclination of one of the principal axes toOX is given by

2 =() Eqn (1) The experimental determination of the principal axes of a given section is based on the

fact that when the load passes through the shear centre and is in the direction of one of the

principal axes of the section, the entire section under the load deflects in the direction of theload only.

APPARATUS REQUIRED:

A thin uniform cantilever Z section as shown in figure. At the free end extension pieces are attached on either side of the web to facilitate vertical loading.

Two dial gauges (to be mounted vertically and horizontally as in figure). This enablesthe determination of displacements u and v.

Two hooks are attached to the extension pieces to apply the vertical load W V. A string and pulley arrangement to apply the horizontal load W H.

A steel support structure to mount the channel section as cantilever.

FORMULA USED:

1. Theoretical calculation

2 =2( ) Where, Inclination of one of the principal axes

Moment about X axis

Moment about Y axis Product of inertia

Exercise No.: 01Unsymmetrical Bending of Beams

Date:


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TABULATION:

WV = Height, h = Breadth, b = Thickness, t =

Sl. No. Horizontal LoadW H

Dial gauge readings Remarks

u v

01

02

03

04

05

06

07

08

09

10

11


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2. Experimental calculation

=tan Where,

Vertical load of weight

Horizontal load of weightPROCEDURE:1. Mount two dial gauges on the tip section to measure the horizontal and vertical

deflections of a point on it.2. Apply the vertical load W V (about 2.4 kg, including two hooks of each 200 gm).3. Read u and v the horizontal and vertical deflections respectively, at the chosen point.4. Increase the load W H in steps of about 300 gm (for the first case 100 gm + 200 gm

hook) from zero to a maximum of about 3 kg noting down in each case the values of uand v. Repeat the procedure and check for consistency in measurements.

5. Plot the graphs vs and find the intersection of this curve with a straight linethrough the origin at 45. (Note: The X and Y scales must be chosen to be same for thegraph).

6. Calculate the inclination of one of the principal axes to the web as =tan where W V and W H correspond to the point of intersection.

7. Calculate the inclination using Eqn (1).

RESULT:

Thus the principal axis of an unsymmetrical section has been determined.


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W a W b

Dial gauge Dial gauge

Wa + W b = W V

Determination of Shear Center


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AIM:To determine the shear centre of an open section.

THEORY:

For any unsymmetrical section there exists a point at which any vertical force does not produce a twist of that section. This point is known as shear centre.

The location of this shear centre is important in the design of beams of open sectionswhen they should bend without twisting, as they are weak in resisting torsion. A thin walledchannel section with its web vertical has a horizontal axis of symmetry and the shear centrelies on it. The aim of the experiment is to determine its location on this axis if the applied shearto the tip section is vertical (i.e., along the direction of one of the principal axes of the section)and passes through the shear centre tip, all other sections of the beam do not twist.

APPARATUS REQUIRED:

A thin uniform cantilever beam of channel section as shown in the figure. At the freeend extension pieces are attached on either side of the web to facilitate vertical loading.

Two dial gauges are mounted firmly on this section, a known distance apart, over thetop flange. This enables the determination of the twist, if any, experienced by thesection.

A steel support structure to mount the channel section as cantilever.

Two loading hooks each weighing about 200 gm.

FORMULA USED:

1. Theoretical calculation

=36 Where,

h height of the flange b

width of the flange

2. Experimental calculation

From the graph e versus (d 1-d2)

PROCEDURE:

1. Mount two dial gauges on the flange at a known distance apart at the free and of the beam. Set the dial gauge readings to zero.

2. Place a total of, say two kilograms load at A (loading hook and nine load pieces willmake up this value). Note the dial gauge readings (nominally, hooks also weigh a 200gm each).

Exercise No.: 02Shear Centre of Open Sections

Date:


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TABULATION:

Length, L = Height, h = Breadth, b = Thickness, t =

WV = (W a+ W b) Distance between the two hook sections (AB) =

Sl. No. W a W b Dial gauge readings

(d 1-d 2)

=

d 1 d 2

01

02

03

04

05

06

07

08

09

10

11


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3. Now remove one load piece from the hook at A and place another hook at B. Thismeans that the total vertical load on this section remains 2 kg. Record the dial gaugereadings.

4. Transfer carefully all the load pieces and finally the hook one by one to the other hooknoting each time the dial gauge readings. This procedure ensures that while the

magnitude of the resultant vertical force remains the same its line of action shifts by aknown amount along AB every time a load piece is shifted. Calculate the distance eof the line of action from the web thus:

= 5. For every load case calculate the algebraic difference between the dial gauge readings

as the measure of the angle of twist suffered by the section.6. Plot against e and obtain the meeting point of curve (a straight line in this case) with

the e -axis (i.e., the twist of the section is zero for this location of the resultant verticalload). This determines the shear centre.

Theoretical location of the shear centre = + * Though a nominal value of 2 kg for the total load is suggested it can be less. In that event thenumber of readings taken will reduce proportionately.

GRAPH:

Plot e versus (d 1-d2) curve and determine where this meets the e axis and locate the

shear centre.

PRECAUTIONS:

I. For the section supplied there are limits on the maximum value of loads to obtainacceptable experimental results. Beyond these the section could undergo excessive

permanent deformation and damage the beam forever. Do not therefore exceed thesuggested values for the loads.

II. The dial gauges must be mounted firmly. Every time before taking the readings tap theset up (not the gauges) gently several times until the reading pointers on the gaugessettle down and do not shift any further. This shift happens due to both backlash and

slippages at the points of contact between the dial gauges and the sheet surfaces andcan induce errors if not taken care of. Repeat the experiments with identical settingsseveral times to ensure consistency in the readings.

RESULT:

The shear centre obtained experimentally is compared with the theoretical value.


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W a W b

Dial gauge Dial gauge

Determination of Shear Center- Closed section


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AIM:To determine the shear centre of a closed section.

THEORY:

For any unsymmetrical section there exists a point at which any vertical force does not produce a twist of that section. This point is known as shear centre.

The location of this shear centre is important in the design of beams of closed sectionswhen they should bend without twisting. The shear centre is important in the case of a closedsection like an aircraft wing, where the lift produces a torque about the shear centre. Similarlythe wing strut of a semi cantilever wing is a closed tube of aerofoil s ection. A thin walled Dsection with its web vertical has a horizontal axis of symmetry and the shear centre lies on it.The aim of the experiment is to determine its location on this axis if the applied shear to the tipsection is vertical (i.e., along the direction of one of the principal axes of the section) and passesthrough the shear centre tip, all other sections of the beam do not twist.

APPARATUS REQUIRED:

A thin uniform cantilever beam of D section as shown in the figure. At the free endextension pieces are attached on either side of the web to facilitate vertical loading.

Two dial gauges are mounted firmly on this section, a known distance apart, over the

top flange. This enables the determination of the twist, if any, experienced by thesection. A steel support structure to mount the channel section as cantilever. Two loading hooks each weighing about 200 gm.

PROCEDURE:

1. Mount two dial gauges on the flange at a known distance apart at the free and of the beam. Set the dial gauge readings to zero.

2. Place a total of, say two kilograms load at A (loading hook and nine load pieces willmake up this value). Note the dial gauge readings (nominally, hooks also weigh a 200

gm each).3. Now remove one load piece from the hook at A and place another hook at B. Thismeans that the total vertical load on this section remains 2 kg. Record the dial gaugereadings.

4. Transfer carefully all the load pieces and finally the hook one by one to the other hooknoting each time the dial gauge readings. This procedure ensures that while themagnitude of the resultant vertical force remains the same its line of action shifts by aknown amount along AB every time a load piece is shifted. Calculate the distance eof the line of action from the web thus:

=

5. For every load case calculate the algebraic difference between the dial gauge readingsas the measure of the angle of twist suffered by the section.

Exercise No.: 03Shear Centre of Closed Sections

Date:


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TABULATION:

Length, L = Height, h = Thickness, t =

WV = (W a+ W b) Distance between the two hook sections (AB) =

Sl. No. W a W b Dial gauge readings

(d 1 - d 2)

=

d 1 d 2

01

02

03

04

05

06

07

08

09

10

11


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6. Plot against e and obtain the meeting point of curve (a straight line in this case) withthe e -axis (i.e., the twist of the section is zero for this location of the resultant verticalload). This determines the shear centre.

* Though a nominal value of 2 kg for the total load is suggested it can be less. In that event thenumber of readings taken will reduce proportionately.

GRAPH:

Plot e vs (d 1-d2) curve and determine where this meets the e axis and locate the shearcentre.

PRECAUTIONS:

I. For the section supplied there are limits on the maximum value of loads to obtainacceptable experimental results. Beyond these the section could undergo excessive

permanent deformation and damage the beam forever. Do not therefore exceed thesuggested values for the loads.

II. The dial gauges must be mounted firmly. Every time before taking the readings tap theset up (not the gauges) gently several times until the reading pointers on the gaugessettle down and do not shift any further. This shift happens due to both backlash andslippages at the points of contact between the dial gauges and the sheet surfaces andcan induce errors if not taken care of. Repeat the experiments with identical settingsseveral times to ensure consistency in the readings.

RESULT:

The shear centre obtained experimentally is compared with the theoretical value.


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Constant Strength Beam


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AIM:To determine the stress at various locations along the length of a constant strength beam

to show that they are equal and compare with theoretical values.

THEORY:

The aerospace structures engineer is constantly searching for types of structures whichwill save structural weight and still provide a structure which is satisfactory from a fabricationand economic standpoint. One such structure is constant strength beam. A beam in whichsection modules varies along the length of the beam in the same proportion as the bendingmoment is known as constant strength beam. In this case the maximum stress remains constantalong the length of the beam.

b width of the beamL length of the beamh depth of the beamSection modulus, ==

== Let the width of the beam be constant and the depth varies. Then

==6=6 = = .. Eqn (1)

APPARATUS REQUIRED:

A constant strength beam in which the depth varies as in Eqn (1) and made ofaluminium. Strain gauges, strain indicator and weights with hook.

PROCEDURE:

The constant strength beam is fixed as a cantilever strain gauges are fixed near the root,at and . The strain gauges are fixed both on the top and bottom surfaces at each locationto increase the circuit sensitivity of the strain gauge circuit. Hence half bridge used in the strainindicator to measure the strain at each location (strain = strain meter reading x 2). The beamloaded gradually in steps of 2 kg up to 10 kg by placing the weights slowly in the hook nearthe tip of the cantilever (loading hook weight 0.25 kg is to be added). The strain gauge readingsare noted for every 2 kg at locations A, B, C and tabulated as given below.

Strain gauge resistance = 350 ohmGauge factor = 2Youngs modulus, E = 70 GPa

Exercise No.: 04Constant Strength Beam

Date:


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TABULATION:

Sl. No. Weight(Kg) = (MPa) = (MPa) = (MPa)01

02

03

04

05


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THEORETICAL CALCULATION

At point A:

Distance of point A from loading point =

Depth of the beam =

Width of the beam =

Moment of inertia =

Moment =

= =At point B:

Distance of point B from loading point =

Depth of the beam =

Width of the beam =

Moment of inertia =

Moment =

= =

At point C:

Distance of point C from loading point =

Depth of the beam =

Width of the beam =

Moment of inertia =

Moment =

= =RESULT:

The experimental values of the stress are compared with the theoretical values.


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AIM:To determine the principal stresses and principal planes of a hollow circular shaft due

to combined loading.

THEORY:

The most common combined load system encountered in structural design is probablythat are due to bending and torsion. In an aircraft wing the lift acting at the centre of pressure

produces a torque about the elastic axis and varying bending moment along the wing span. Tounderstand their combined effect a similar specimen, namely a hollow cylinder is subjected toa bending and torsion.

For an elastic structure, = Where, Bending stress (N/m 2)M Bending moment (N-m)y Distance of the layer from the neutral axis (m)I Moment if Inertia (m 4)

=( ) The shear stress due to torsion

= Where,

Shear stress (N/m 2)T Torque applied (N-m)R radius of the shaft (m)J Polar moment of Inertia (m 4) = 32 ,=+ ( ) (1),= (2),= ( )[ ] (3)

Exercise No.: 05Combined Loading

Date:


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tan2== (4)Where,

Principal angle

APPARATUS REQUIRED:

Hollow circular shaft fixed as a cantilever, weight hanger with slotted weights, straingauges, connecting wires, strain indicator and micrometre.

PROCEDURE:

Two strain gauges are fixed near the root of the tube fixed as a cantilever, one on thetop fibre and the other at the bottom to measure the bending strain. Another strain gauge isfixed at the same location on the neutral axis at 45 to measure the shear strain. Similarly threemore strain gauges are fixed at the middle of the length to verify the result at various locationsof the tube. The strain gauges on the top and bottom of the tube are connected to half bridgecircuit in the strain indicator to increase the circuit sensitivity, since the tension andcompression get added up. The strain gauge at 45 is connected to the quarter bridge of thestrain indicator to measure the shear strain. The outside diameter of the tube is measured usingvernier callipers. Weights are added to the hook attached to the lever in steps of 2 kg and thestrain gauge readings are noted from the strain indicator for each load. From the strains the

bending stress, shear stress are calculated and hence principal stresses and principal angle arecalculated. These values are compared with theoretical values.

NOTE:

For half bridge the strain readings are multiplied by 2 and for Quarter Bridge by 4 toget the actual strains.

RESULT:

Bending stress at the root (A) =

Shear stress at (B) =

Experimental:

Principal stresses at the root =

Principal angle at the root =

Theoretical:

Principal stresses at the root =

Principal angle at the root =


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Wagner Beam


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AIM:To investigate and study the behaviour of a semi-tension field beam.

THEORY:

The development of a structure in which buckling of the web is permitted with the shearloads being carried by diagonal tension stresses in the web is a striking example of the departureof the design of aerospace structures from the standard structural design methods in other fieldsof structures, such as beam design for bridges and buildings. The first study and research onthis new type of structural design involving diagonal semi-tension field action in beam websdone by Wagner and hence Wagner beam.

As thin sheets are weak in compressions, the webs of the Wagner beam will buckle ata low value of the applied vertical load. The phenomena of buckling may be observed bynothing the wrinkles that appear on the thin sheet. As the applied load is further increased, thestress in the compression direction does not increase, however the stress increase in the tensiondirection. This method of carrying the shear load permits the design of relatively thin webs

because of high allowable stresses in tension.

According to the theory developed by Wagner, the diagonal tensi le stress t in the thinweb is given by the expression

= ............... Eqn (1)Where, W Shear loadd Distance between the CG of the flangest Thickness of the web Angle at which wrinkling occurstan=++ ............... Eqn (2)

Where, b Distance between stiffenersAF Area of flangeAS Area of stiffener

Exercise No.: 06Structural Behaviour of a Semi-Tension Field Beam

Date:


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TABULATION:

t = b = d = = AF = A S = E =

Sl. No. Weight(Kg) t F S t = 4E t F = 4E F S = 4E S

01

02

03

04

05


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Stress in the Flange = ............ Eqn (3)Stress in the stiffener

= tan ............ Eqn (4)

APPARATUS REQUIRED:

A stiffened thin-webbed cantilever beam held in a suitable frame, strain gauges, strainindicator, hydraulic jack, load cell and load indicator.

PROCEDURE:

The wrinkling angle is calculated using the Eqn (1) and a strain gauge is fixed at thisangle in the web. Strain gauges are also fixed on the flanges and a stiffener to measure theirrespective stresses. The load is applied gradually in steps of 100 kg using the hydraulic jack.For each load the load indicator reading, strain indicator reading corresponding to each straingauge is noted. Precaution is taken so that the beam does not undergo any permanentdeformation. Hence the beam is not loaded up to wrinkling load. The readings are tabulated asgiven below

The strain gauges are connected in Quarter Bridge and hence the strain indicatorreadings are to be multiplied by 4 to obtain the actual strain.

RESULT:

t, F and S values are calculated theoretically using Eqns (1),(3) and (4) andcompared with the experimental values given in the table.


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Fig. 7.1. A cantilever beam

Fig. 7.2. The cantilever beam under free vibration

Fig. 7.1 shows of a cantilever beam with rectangular cross section, which can besubjected to bending vibration by giving a small initial displacement at the free end; andFig. 7.2 depicts of cantilever beam under the free vibration.


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AIM: To obtain natural frequencies of a cantilever beam up to the second mode,experimentally; and to observe the response of the system subjected to a small initialdisturbance and virtualization of the experiment. This virtual experiment is based on a themethat the actual experimental measured vibration data are used.

THEORY:

Free vibration takes place when a system oscillates under the action of forces inherentin the system itself due to initial disturbance, and when the externally applied forces are absent.

The system under free vibration will vibrate at one or more of its natural frequencies, whichare properties of the dynamical system, established by its mass and stiffness distribution.

In case of continuous system the properties of the system are the function of spatialcoordinates. The system has infinite number of degrees of freedom and infinite number ofnatural frequencies.

In actual practice there is always some damping (e.g., the internal molecular friction,viscous damping, aerodynamical damping, etc.) present in the system which causes the gradualdissipation of vibration energy, and it results gradual decay of amplitude of the free vibration.Damping has very little effect on natural frequency of the system, and hence, the calculations

for natural frequencies are generally made on the basis of no damping. Damping is of greatimportance in limiting the amplitude of oscillation at resonance.

The relative displacement configuration of the vibrating system for a particular naturalfrequency is known as the Eigen function in continuous system. The mode shape correspondingto lowest natural frequency (i.e. the fundamental natural frequency) is called as the fundamental(or the first) mode. The displacements at some points may be zero. These points are known asnodes. Generally nth mode has (n-1) nodes (excluding end points). The mode shape changesfor different boundary conditions of a beam.

MATHEMATICAL ANALYSIS:For a cantilever beam subjected to free vibration, and the system is considered as

continuous system in which the beam mass is considered as distributed along with the stiffnessof the shaft, the equation of motion can be written as (Meirovitch, 1967),

= 1 Where, E is the modulus of rigidity of beam material, I is the moment of inertia of the

beam cross-section, Y(x) is displacement in y di rection at distance x from fixed end, is thecircular natural frequency, m is the mass per unit length , m = A(x), is the material density,x is the distance measured from the fixed end.

Exercise No.: 07Determination of Natural Frequencies of Cantilever Beams

Date:


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Fig. 7.3. The first three undamped natural frequencies and mode shape of cantilever beam


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We have following boundary conditions for a cantilever beam.

=0, =0, =0 = ,=0, =0

For a uniform beam under free vibration from equation (1), we get

=0 where,

=

The mode shapes for a continuous cantilever beam is given as

={sin sinhsin sinhcos coshcos cosh} where,

=1,2,3 = A closed form of the circular natural frequency , from above equation of motionand boundary conditions can be written as,

= where,

=1.875,4.694,7.885

RESULT:

First Natural Frequency Second Natural Frequency Third Natural Frequency

= = =


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Fig. 8.1. Disk in compression

Fig. 8.2. Stress distribution along horizontal diameter


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AIM:To obtain the stresses in circular discs and beams using photo elastic techniques.

THEORY:

A common calibration specimen is the circular disk of diameter D and thickness loaded in diametral compression (Fig. 8.1).The horizontal and vertical normal stresses along the x axis are principal stresses

because the shear stress vanishes due to symmetry about the x axis. Also, is positive,while is negative. We therefore take = and = so as to render 0. Fromtheory of elasticity, the solutions for the normal stresses along the horizontal diameter are (afterDally and Riley 1991).

=211

=6

1 1131

where

==2 These stresses are plotted in Fig. 8.2. Along the horizontal diameter, the maximum

difference occurs at the centre, that is, at = 0. At this point,=8

Combining this result with the basic photo elastic relation gives

= =8 or =8

Notice that the specimen thickness does not appear in this equation. The reason isthat the relative retardation is proportional to , but for a given force P, the stresses areinversely proportional to . The net effect is a result for that is independent of .

Exercise No.: 08Stresses in Circular Discs using Photo elastic Techniques

Date:


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Fig. 8.3. Light-field isochromatics in a diametrally loaded circular disk.

Fig. 8.4. Enhanced image using only the green component of the light used in Fig. 8.3.


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A photograph of a light-field isochromatic pattern for a diametrally loaded disk madeof PSM-1 is shown in Fig. 8.3. For this specimen, the diameter D was 63.50 mm (2.500 in.),and the load was 1.33 kN (298 lb). The value of N at the centre of the disk, as seen in Fig. 8.3,is approximately 7.0. Therefore the fringe constant for this material is approximately

=8 = 8 0.63513307=761.94 A more accurate way of determining using this specimen is to record several readingsof increasing load P as the fringe value N at the centre takes on integer or half-integer values.

The saddle shape of the central fringe allows rather precise determination of N for this purpose.Then P is plotted as a function of N, and the best straight-line fit of the data is used to determinethe ratio P / N to be used in fringe constant equation.

The disk in diametral compression is a favourite specimen for calibration because it issimple to fabricate (at least with a template); it is easy to load; it is not likely to fracture; it

produces a fringe pattern that, in the region of interest, is insensitive to edge imperfections; andit is simple to analyse. It also tests the limit of fringe density that can be recorded

photographically, by producing very large fringe orders in the vicinity of the contact regions.

The image in Fig. 8.3 was obtained with a mercury-vapour light source, which is richin green light, but which also contains other colours as well. A Tiffen #58 Green filter was

placed on the 35 mm camera to reduce the transmission of the other colours. Kodak Gold ASA200 colour film was used to record the image at f/8 with an exposure of 0.7 s. This arrangementresults in distinct fringes up to about N = 15, which is adequate for most work in photoelasticity.

A somewhat enhanced image is shown in Fig. 8.4. This image was produced from thesame negative as that used to produce Fig. 8.3. However, only the green component of thered-green-blue (RGB) digital scan was retained, and this component was then enhanced byincreasing the contrast.

Fringe orders up to about N = 20 can be discerned in this figure. The low-order values of N aremarked along the horizontal diameter. Note that the centre of the specimen is the location of atrue saddle point in the function : to the left and right of this point, the functiondecreases, and above and below this point, the function increases. Such saddle points arecommon in photo elastic patterns.

RESULT:

The value of the stresses in Circular disc are computed using Photo elastic technique.The stress distribution in a disk in diametral compression is unique in that the fringe number Nis equal to zero everywhere along the unloaded boundary.


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Aircraft Structures Lab II Manual for AUC R2008_S

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