SOLUTION APPROACH FOR NONLINEAR VISCOELASTIC PROBLEMS FOR POLYMER MATERIALS

Although the experiments are restricted to small strain, it still reveals significant nonlinear viscoelastic behavior for polymer materials. However, the assumption of linear viscoelasticity is often used because the difficulties in the analysis at present. On the bases of the previous paper, a new principle for finding solutions of physically nonlinear (or linear) viscoelastic porblems for polymers is proposed . By means of which, the solution of a nonlinear viscoelastic problem can be obtained if the corresponding nonlinear elastic problem is known. The idea of this principle is entirely different from the traditional idea for correspondence principle in linear viscoelasticity. Not the similarity between the elastic and the viscoelastic constitutive relations is utilized. Rather, the recoverability from the nonlinear viscoelastic response to the nonlinear instantaneous elastic response will be used. It is shown by the experiments for improved polypropylene that this principle is valid and is applicable for such class of materials.