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Table 1: Recorded values of Strain( )

Longitudinal 1 ( ) Lateral 2 ( )

Initial (un-deflected) 4000 3536

Final (deflected) 6433 4286

Net Strain

= - i

2433 750

Calculation:

Correction of lateral stain for transverse sensitivity:

Note that the longitudinal strain on the bottom of the beam is negative. Therefore,

Figure 1: Correction chart used to find the Correction factor

Table 2: Actual values of Poissons ratio

1

32.0750

:'

780750

04.1

:

2.1

244.3750

)2433(

1

2

1

=

=

==

=

+=

==

Cv

ratiosPoissonofnCalculatio

CstrainlateralCorrected

C

chartcorrectiontheFrom

Kt

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Poissons ratio is the ratio of transverse strain to the axial strain ,where transverse strain

is the deformation in the direction of application of force, while the axial strain is

deformation in the directions perpendicular to action of force . The specimen has to be

isotropic to get satisfactory results, which means the measured properties do not vary

with the direction of measurement. The Poissons ratio also proves that there is no

change in volume of a substance when it changes shapes under stress i.e. if for example

a beam is stretched in the direction of length causing an increase in length, while the

width and thickness of the beam will shrink to counter the effect of this increase in

length there by keeping volume constant. Notice that in the experiment the strain gages

where placed on the upper and lower surface at the same point to ensure both reading of

lateral and longitudinal strain are of the same point. This is because the degree of

deformation change at different points depending on the distance from the point where

the force is applied.

Conclusion

The Poissons ratio calculated using measured strain values is 0.32 which is very near

to the value of Poissons ratio of aluminum alloy which is 0.33 as shown in table 2.

3