Extensive validation of a thermodynamically consistent, nonlinear viscoelastic model for glassy polymers

The nonlinear thermoviscoelastic formalism presented in the preceding paper is validated with four amorphous polymer systems. Validation is performed over a broad range of relaxation phenomena in the glass transition region, including the temperature and rate-dependence of the stress–strain behavior through yield, volume and enthalpy relaxation, and stress relaxation during multi-step loading histories. The objective is to obtain quantitative agreement between the constitutive theory and all experimental results using one set of model parameters for each material system. The nonlinear viscoelastic formalism is shown to predict the wide range of behavior observed experimentally, indicating that the formalism does capture the essential physics of glassy polymers. Moreover, the material parameters required in the constitutive formalism can be readily obtained from independent experiments and are relatively insensitive to how these parameters are determined experimentally from the various characterization techniques.