Poisson's ratio is a measure of the Poisson effect, that describes the expansion or contraction of material in directions perpendicular to the direction of loading. The deformation that occurs is mainly concerned with the elastic deformation in that the load applied to the material will not cause permanent change. This is​ the main reason why this phenomenon is highly apparent in elastomers and rubbers.

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Represented by the equation:

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When you apply load to the material it will inherently expand in a direction perpendicular to the applied load.

• The direction in which the load is being applied is called the longitudinal axis

• The direction perpendicular to the load is called the lateral axis

When you apply load to a material it will also deform in the lateral directions

 

Essentially Poisson's ratio explains why when you apply uniaxial loading to a rubber band the material extends length-wise but the width shortens

 

 

 

Interpretation of Poisson's Ration Values

 

The value of the Poissons ratio will range from -1 to 0.5.

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When the Poisson's ratio is less than 0.5 but greater than 0

• Its will expand longitudinally and shorten laterally

• The majority of materials will have a Poisson ratio within this region

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When Poisson's ratio is equal to zero

• No change will occur in response to the applied load

• This means the volume of the material does not undergo any volumetric change when the longitudinal load is applied

• This explains why material such as cork can fulfill their task efficiently

  • When compressed the volume of the cork does not change allowing to be placed within the neck of a bottle ​

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When Poisson's ratio is a negative value

• It will expand longitudinally and expand laterally

• Contrary to what occurs  in most instances a material with a negative value of Poisson's ratio will expand when a tensile load is applied a contract when a compressive load is applied