Plastic deformation in glassy polymers by atomistic and mesoscopic simulations

Abstract

We present here a short summary of two rather different, but complementary,simulations of plastic deformation in a flexible chain glassy polymer.In the first, atomistic simulation, a molecular structure model isused in which well-established force fields between atoms and atomgroups on a typical chain polymer are introduced to account for themost relevant molecular degrees of freedom that govern both structuraland shear relaxations. The principal result of this simulation whichhas been described in great detail elsewhere [Mott et al., Philos.Mag. 67, 931?978 (1993a)] is that shear relaxations are in the formof abrupt shear transformations occurring in volume elements of ~10nm size and resulting in transformation shear strains of ~2%. Thissimulation has established that the chemically specific conformationalconstraints are internal to the volume elements and that the interactionof the elements with their surroundings is elastic, suggesting thatthe phenomenon can be meaningfully simulated by a two-dimensionalmesoscopic model. In the second part of the present communicationwe summarize the most important findings of the extensive two-dimensionalmesoscopic simulation which we [Bulatov and Argon, Model. Sim. Mater.Sci. Eng. 2, 167?184 (1994a); 185?202 (1994b); 203?222 (1994c)] haveperformed. These findings include the important effects of disorderrelated misfit stresses in governing both quasihomogeneous flow atelevated temperatures and localized shear flow at lower temperatures.In addition, we demonstrate that these misfit stresses are the keyingredient that governs the initial deformation transients, as wellas the well-known distributed kinetics of the deformation processin amorphous media in general.