Poisson's ratio

When a sample of material is stretched in one direction, it tends to get thinner in the other two directions. Poisson's ratio (ν), named after Simeon Poisson, is a measure of this tendency. It is defined as the ratio of the strain in the direction of the applied load to the strain normal to the load. For a perfectly incompressible material, the Poisson's ratio would be exactly 0.5. Most practical engineering materials have ν between 0.0 and 0.5. Cork is close to 0.0, most steels are around 0.3, and rubber is almost 0.5. Some materials, mostly polymer foams, have a negative Poisson's ratio; if these auxetic materials are stretched in one direction, they become thicker in perpendicular directions.

Related Topics:
Simeon Poisson - Strain - Auxetic material

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A Poisson's ratio greater than 0.5 does not make sense because at a certain strain the material would reach zero volume, and any further strain would give the material "negative volume".

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