All-atom molecular dynamics study of the impact fracture of glassy polymers. III: Compressive fracture of PC and PMMA

Abstract

The compressive fracture of glassy polymers was investigated by performing all-atomistic molecular dynamics calculations for poly (methyl methacrylate) (PMMA) and polycarbonate (PC). The microscopic behaviors such as conformation changes of PMMA were different from that of PC by the analysis of one- and two radial distribution functions and bond breakages. Both brittle PMMA and ductile PC underwent ductile fracture when compressed and exhibited stress-strain curves comparable to those obtained experimentally. The compression process demonstrated a similar but not identical mechanism to extension: first, strain-induced affine deformation resulted in volume reduction in the elastic deformation; second, accumulated stress caused plastic deformation and strain softening accompanied by volume expansion; third, strain hardening occurred, but because of van der Waals repulsion instead of the entanglement networks. The volume expansion during strain softening showed no correlation with the increase in the dihedral transition rate. Structural anisotropy was observed as the strain increased, leading to the alignment of the polymer chain to the plane perpendicular to the compression direction and anisotropic density distribution.