Fracture of glass bead/epoxy composites: on micro-mechanical deformations

To understand the fracture behavior of inorganic particle filled polymers, glass bead filled epoxies having different glass bead contents and sizes were prepared as model systems. Although their macroscopic fracture behavior was brittle, diffuse matrix shear yielding and micro-shear banding were found to occur around crack paths. Besides these plastic deformations, debonding of glass beads, step formation on fracture surface, and birefringence due to thermal residual misfit between glass beads and matrix were identified and studied. The fracture toughness and modulus of composites generally increased with increase in the volume fraction of glass beads, Micro-shear band zone size, debonding zone size, and the areal density of steps also followed increases in the volume fraction. The effect of glass bead size on fracture toughness and modulus was not significant, but the areal density of steps was found to increase as the size decreased. Differential thermal contraction between glass beads and matrix was found to cause the thermal residual misfit, resulting in birefringence around glass beads. Microscopy studies revealed that this thermal residual misfit might not have an extensive influence on crack propagation. (C) 2000 Published by Elsevier Science Ltd.