A material's elastic limit is the greatest stress that can be applied to it without causing plastic (permanent) deformation. When a material is stressed to a point below its elastic limit, it will return to its original length once the stress is removed.  Once a material is stressed to a point exceeding its elastic limit, it begins to permanently yield, and when the stress is removed the material will not fully return to its original length. The elastic limit is difficult to accurately determine using a universal testing machine, which is why it is generally used for educational purposes rather than in practice by the materials testing industry.

How is Elastic Limit Different from Proportional Limit?

The proportional limit of a material is the point on a stress/strain curve where the linear, elastic deformation region transitions into the non-linear, plastic deformation region. A material's elastic limit can be equivalent to its proportional limit for certain materials, but for others, the stress/strain relationship will become nonlinear before reaching the material's elastic limit.

How is Elastic Limit Different from Yield Strength?

Similar to the elastic limit, the yield strength of a material is the stress that represents the transition point between elastic and plastic deformation. Unlike the elastic limit, which is impractical to precisely determine with a universal testing machine, yield strength can be determined through using various calculation methods accepted by the testing industry and outlined in a material's ASTM or ISO testing standard.