Simulation of the plastic behavior of amorphous glassy bis-phenol-A-polycarbonate

A protocol for studying the plastic deformation of amorphous glassy polymers is presented. The protocol is based on a viable computational procedure which combines constant-stress molecular dynamics simulations and fixed-cell energy minimizations, followed by kinetic, configurational, and energy analyses. It is shown that the computational results can be accounted for within a "potential energy landscape" theoretical framework, in which the plastic transition is interpreted as a crossing between and a collapse onto each other of "ideal (thermodynamic) structures." The procedure is applied to bis-phenol-A-polycarbonate (BPA-PC), but is equally valid for a wide variety of polymeric species. Allowing for the limited size of the simulation cell, the high strain rate, and the fact that the simulation are conducted at low temperature, the values of the density, Young's modulus, yield strain, yield stress, activation energy, and activation volume are in fair agreement with the experimental data on BPA-PC. The analysis of the results shows that the plastic relaxation for this polymer has both a collective and cooperative character (as in classical percolation theories), involves a significant fraction of the simulation cell, and can be viewed as a "nanoscopic shear band."