Abstract: In this paper, a simple instantaneous elastic constitutive relation for nonlinear viscoelastic materials is obtained by using the elasticity recovery correspondence principle in nonlinear visc oelastic constitutive theory.The result that the nonlinear viscoelastic constitutive relation being marked by the instantaneous elastic constitutive relation can correctly describe the mechanics behaviors of nonlinear viscoelastic materials is verified by comparison between the the-oretic calculated results and experimental data about the experiments under different strain rate levels for improved polypropylene.

Key words:  , instantaneous elastic constitutive relation, nonlinear viscoelastic constitutive relation, elasticity recovery correspondence principle, relaxat ion modulus, creep compliance