Modelling nonlinear viscoelasticity and damage in amorphous glassy polymers

Constitutive equations are derived for the nonlinear viscoelastic behavior of amorphous glassy polymers in the subyield region. A polymer is thought of as an ensemble of cooperatively rearranged regions trapped in cages. In the phase space, a cage is modeled as a potential well, where a flow unit hops as it is thermally activated at random times. The viscoelastic response is treated as rearrangement of flow units. A rearrangement event occurs when a region reaches some liquid-like state in a hop. Damage of a polymer is modeled as breakage of van der Waals forces between monomeric units. It happens when the nominal strain in a relaxing region exceeds some threshold level. Stress-strain relations for a glassy polymer and a governing equation for the damage evolution are developed and verified by comparison with experimental data. Fair agreement is demonstrated between results of numerical simulation and observations for polycarbonate.