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) 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 materialss are stretched in one direction, they become thicker in perpendicular directions. Poisson's ratio is named for Simeon Poisson.
External links Meaning of Poisson's ratio Negative Poisson's ratio materials Poisson's ratio
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