Modeling of nonlinear viscoelastic-viscoplastic behavior of glassy polymers based on intramolecular rotation of molecular chains

In recent years, there has been progress in the development of constitutive models for reproducing the mechanical properties of glassy polymers, but there are limitations to conventional models, such as increased complexity and the number of material parameters. In this study, a new model was proposed to describe the nonlinear viscoelastic-viscoplastic behavior under loading, unloading, and cyclic loading conditions at temperatures below the glass transition temperature. The anelastic strain was considered in addition to elastic strain and plastic strain, which is based on three states: a stable state, a metastable state in tension, and a metastable state in compression. The numerical results obtained with the present model were compared with those obtained with the latest existing model and with the experimental results to investigate the ability to model both viscoelasticity and viscoplasticity. The proposed model stands out for its capacity to predict nonlinear viscoelasticity and viscoplasticity for various loading conditions with only simple thermal activation processes. The 22 material parameters required are fewer than those of recent models used for comparison. This is because the proposed model expresses the viscoelastic phenomena during loading and unloading in a unified manner.