Expt 3 - Photo Elasticity

ME 218: SOLID MECHANICS LABORATORY

PHOTOELASTICITY EXPERIMENT NO.3

BATCH: A8 07010042-07010046

PHOTOELASTICITY EXPERIMENT NO.3

AIM

To determine the material fringe constant of the given photo elastic material and use it to find stress concentration factor for a particular geometry.

A P PA R A T U S 1. 2. 3. 4. 5. 6. 7.

Araldite specimens ( 2 no.s ) Two plane polarisers. Analyser plate. Two quarter wave plates White light source (concentrated) Arrangement for load application (tensile) Vernier calipers. T H E O RY

Photo-elastic techniques are of great significance so far as the determination of a stress state of specimen under load is considered. Shapes with arbitrary cross sections can be analyzed under this method to obtain lines of constant stress on the section. Thus it is possible to determine the state of the stress in the entire section at the same time, contrary to the case with strain gauges. This ,makes this a very useful tool.

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WOR K ING FO R MU L A E

1.σ 11 - σ 22= n * Fσ Here, σ 22 = 0 ( Plane stress condition ) 2.σ 11 /(P/A) = SCF Where, σ  Principle stress n  Fringe order F σ  Material fringe constant P/A  Average stress SCF  Stress Concentration Factor.

SPECIMEN DIAGRAMS

Sample 1

Sample 2

Table 3.1 Sample Length(mm) Breadth(mm) Thickness(mm) Radius(mm) No. 1 82.75 34 11.2 NA 2 83.04 35.5 11..2 12.4

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OBSERVATION

Table 3.2 :Colour

Fringe Order

Grey

0.28

Yellow

0.6

Orange

0.8

Pink

0.9

Blue

1.08

Green

1.22

Yellow

1.6

Table 3.3 :Sample 1 – Area = 0.00038 m2 S.No.

Load (lbs)

1

0

2

1

3

3.5

4

5

5

7

6

Color

Load (N)

Stress

Fσ

0

Fringe Order 0.28

0

Transparent

4.45

11697.36

0

0

Pale Yellow

15.57

40921.11

0.42

97431.21

22.25

58473.68

0.6

97456.13

Orange

31.15

81578.94

0.8

101973.7

9

Pink

40.05

105263.2

0.9

116959.1

7

10

Blue

44.5

116973.7

1.08

108309

8

11

Green

48.95

128657.9

1.22

105457.3

Grey

Yellow

Sum of Fσ = ∑ Fσ Average value of Fσ = ∑ Fσ/8 = 78448.2 Pa

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0

Table 3.4 :Sample 2 – Area = 0.0042 m2 S.No.

Color

Load (N)

Stress

1

Load (lbs) 0

σ1=n*Fσ

SCF

0

Fringe Order 0

no color

0

0

0

2

1

grey

4.45

10595.24

0.28

21965.5

2.073148

3

2

yellow

8.9

21190.48

0.6

47068.92

2.22123

4

3

pink

13.35

31785.71

0.9

70603.38

2.22123

5

4

blue

17.8

42380.95

1.08

84724.06

1.999107

6

5

green

22.25

52976.19

1.22

95706.8

1.8066

7

7

yellow

31.15

74166.67

1.6

125517.1

1.692366

Sum of SCF = 12.013 Average of SCF = 1.71624

INFERENCE

The following inferences can be drawn :  The calculated value of Fσ is found to be 78448.2 Pa.  The value of SCF is found to be 1.71624.

P R E C AU T I ON S

1. Make sure that the load applied does not exceed the tensile limits of the araldite specimens. 2. Gently increase and decrease the loads.

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D E TA I L S OF S T U D E N T S

Table 3.5 ROLL NUMBER

NAME

07010042

Repaka Jyoti Swaroop

07010043

Sharath Chandra Pawar

07010044

Puvvada N V Prudhvi Teja

07010045

J G M V Pramod

07010046

Vishnu Narayanan Suresh

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