Coarse-grained molecular dynamics simulation of deformation and fracture in polycarbonate: Effect of loading mode, strain rate, temperature and molar mass

Abstract

Polycarbonate is one of the most promising polymers having potential application as structural materials owing to its prominent properties including lightness, strength and toughness. While computer-aided design of polymer-based engineering products is demanded, obtaining reliable constitutive relations of deformation and fracture has been a challenge. In this study we performed coarse-grained molecular dynamics (CGMD) simulations of polycarbonate to acquire understanding of deformation and fracture mechanism at the molecular level and estimate yield stress under various loading modes. Inter-particle interactions for the CGMD was constructed based on all-atom MD using the COMPASS model, where molecular structures under strain were included. By tensile simulations of four types of loading, namely uniaxial stress, biaxial stress, uniaxial strain and isotropic stress, we calculated yield stress as a function of strain rate. We obtained two master curves of yield stress-strain rate relation; one for the former two loading types and the other for the latter two. The curves can be used for various temperatures by proper shift factors. We also found the effect of molar mass on stress-strain curves; i.e. the larger the molar mass is the larger stress can be attained after yielding, suggesting brittle-ductile transition with increasing molar mass.