A damage-based elastic-viscoplastic constitutive model for amorphous glassy polycarbonate polymers

This paper presents a new damage-based elastic-viscoplastic constitutive model for amorphous glassy polycarbonate (PC) within the framework of irreversible thermodynamics and continuum damage mechanics (CDM). To this end, experimental investigation, theoretical formulation and numerical implementation are performed. In the experiment part, noticeable strain rate and temperature dependent mechanical responses were observed in uniaxial compression tests over a wide range of strain rates and temperatures. Moreover, damage evolution associated with the decreasing elastic modulus was highlighted in cyclic loading-unloading tests. Based on the experimental data, an elastic-viscoplastic model coupled with damage formulation is developed. Constitutive equations, specifically the strain rate and temperature dependent yield criteria, the viscoplastic flow rule and the damage evolution law, are derived from the Helmholtz free energy and the Clausius-Duhem entropy inequality. Introducing an elastic-damage predictor/viscoplastic corrector scheme, a time-discrete frame of the constitutive equations is presented. The nonlinear time-discrete constitutive system is further simplified into a single-scalar Newton-Raphson scheme in view of computational efficiency. The model is then implemented into the finite element program LS-DYNA, by using a user-defined material subroutine (UMAT). The good correlation between model predictions and experimental data demonstrates the capabilities of the proposed model capturing mechanical behavior and damage evolution of PC over a wide range of strain rates and temperatures.