A thermodynamic theory on the nonlinear viscoelasticity of glassy polymers, 1. Constitutive equation

We have developed a nonlinear viscoelastic constitutive equation, which can predict the yield behavior of polymers. This constitutive equation results from the viewpoints that the plastic flow of glassy polymers can be described by a soliton, which is expected to unify the existing concepts for viscoelasticity and yield of glassy polymers, such as dislocation, disclination and free volume. Although our approach is based on molecular concepts and irreversible thermodynamics, it is phenomenological.