Yield strength

stress at which a material exhibits a specific deviation (usually 0.2%) from the standard proportion between stress and strain (Mechanics)

The yield strength or yield point of a material is defined in engineering and materials science as the stress at which a material begins to plastically deform. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed some fraction of the deformation will be permanent and non-reversible. In the three-dimensional space of the principal stresses (), an infinite number of yield points form together a yield surface.
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