7/31/2019 Informal Poisson's Ratio
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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
7/31/2019 Informal Poisson's Ratio
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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
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