### Poisson's Ratio for Materials

Definition:

Poisson's Ratio is the ratio of the transverse to the longitudinal strains under axial stress within the elastic range. It is a negative ratio.

$mathematical expression of Poisson's ratio$

In the expression "$\nu$" is the resulting Poisson's ratio, "$\varepsilon_\mathrm{trans}$" is transverse strain, "$\varepsilon_\mathrm{axial}$" is axial strain.

Poisson's Ratio is named after french physicist Siméon Poisson (1781-1840). When a material is compressed in one direction, it usually tends to expand in the other two directions perpendicular to the direction of compression. This phenomenon is called the Poisson effect.

Typical values of Poisson's Ratio for various commonly used materials are given below:
Poisson's Ratio

Material Poisson's ratio
rubber ~ 0.55
gold 0.42 - 0.44
saturated clay 0.40–0.49
magnesium 0.35
titanium 0.34
copper 0.33
aluminium-alloy 0.32
clay 0.30–0.45
stainless steel 0.30–0.31
steel 0.27–0.30
cast iron 0.21–0.26
sand 0.20–0.45
concrete 0.20
glass 0.18–0.3
foam 0.10–0.40
cork ~ 0.00

Here is a related video about Poisson's Ratio of materials. This video is taken from youtube.com.

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