Editing Poisson's ratio (section)

{{Short description|Measure of material deformation perpendicular to loading}}
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[[File:Poisson ratio compression example.svg|thumb|Poisson's ratio  of a material defines the ratio of transverse strain ({{mvar|x}} direction) to the axial strain ({{mvar|y}} direction)]]
In [[materials science]] and [[solid mechanics]], '''Poisson's ratio''' (symbol: '''{{mvar|ν}}''' ([[Nu (letter)|nu]])) is a measure of the '''Poisson effect''', the [[Deformation (engineering)|deformation]] (expansion or contraction) of a material in directions perpendicular to the specific direction of [[Structural load|loading]]. The value of Poisson's ratio is the negative of the ratio of [[Lateral strain|transverse strain]] to axial [[strain (materials science)|strain]]. For small values of these changes, {{mvar|ν}} is the amount of transversal [[Elongation (materials science)|elongation]] divided by the amount of axial [[Compressive strength|compression]]. Most materials have Poisson's ratio values ranging between 0.0 and 0.5. For soft materials,<ref>For soft materials, the bulk modulus ({{mvar|K}}) is typically large compared to the shear modulus ({{mvar|G}}) so that they can be regarded as incompressible, since it is easier to change shape than to compress. This results in the Young's modulus ({{mvar|E}}) being {{math|''E'' {{=}} 3''G''}} and hence {{math|''ν'' {{=}} 0.5}}.{{cite book |title=Nature and Properties of Engineering Materials |first=D. |last=Jastrzebski |publisher=John Wiley & Sons, Inc |edition=Wiley International |year=1959}}</ref> such as rubber, where the bulk modulus is much higher than the shear modulus, Poisson's ratio is near 0.5. For open-cell polymer foams, Poisson's ratio is near zero, since the cells tend to collapse in compression. Many typical solids have Poisson's ratios in the range of 0.2 to 0.3. The ratio is named after the French mathematician and physicist [[Siméon Poisson]].