Model for mechanical behavior of glassy polymers

Existing constitutive models of glassy polymers are incapable of even qualitatively describing the stress-strain response seen in the course of a four-step deformation experiment (constant strain rate loading-partial unloading-creep-reloading) reported by Dreistadt et al. [1] Specifically, the second stress overshoot observed during reloading is not predicted by the models. There are other features in the thermomechanical behavior of glassy polymers observed experimentally that also cannot be described by existing constitutive models, e.g. deep glass aging. We propose a new model, where an additional physical mechanism accounting for changes in the packing efficiency is included. The model describes material response during basic deformation experiments, the second stress overshoot in the four-step experiment and other features observed experimentally. Further validation experiments for testing the new model will be proposed.

1. Dreistadt et al Materials and Design 30 (2009) 3126