A stress strain diagram or stress strain curve is used to illustrate the relationship between a material's stress and strain. A stress strain curve can be constructed from data obtained in any mechanical test where load is applied to a material and continuous measurements of stress and strain are made simultaneously. Stress strain curves visually display the material's deformation in response to a tensile, compressive, or torsional load.

Depending on the material being tested, a stress strain curve can indicate key properties of the material including its elastic region, plastic region, yield point, and ultimate tensile strength.