Why can't we divide the lateral by the axial strain? Why does the axial strain always have to be the denominator? Would it matter if I was careless and accidently switched them around?
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1$\begingroup$ Will you get the same answer if 5/1 or 1/5? It is called Poissons ratio because he defined it that way. $\endgroup$– Solar MikeJan 4, 2022 at 4:17
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$\begingroup$ Think of it as the ratio of the strain in the direction perpendicular to the applied force and the strain in the direction of the applied force. $\endgroup$– AJNJan 4, 2022 at 12:28
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1 Answer
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Poisson's ratio is defined in the case of uniaxial tensile testing. As such the x axis is in the direction of the loading, while the y and z axis are transverse.
In isotropic materials it doesn't make any difference which axis the material is tested.
However for anisotropic (i.e material that don't behave in the same way in all directions), there are usually defined 3 Poisson's ratios:
- $v_{xy}$
- $v_{yz}$
- $v_{zx}$
(that implies that $v_{ij} = v_{ji}$).
