Polymer stress-strain curve
Elastic Region. In this region stress is proportional to strain and the deformation is completely reversible; Hooke's law is obeyed. The gradient of the straight-line section of the curve gives the elastic modulus of the material. The entropic mechanism for rubber elasticity is explained in the Rubber Elasticity TLP. In practice the elastic region of the curve is unlikely to be perfectly straight; the elastic modulus is taken as the tangent to the first part of the curve.