Effect of rubber interlayers on the fracture of glass bead/epoxy composites

The effectiveness of rubber interlayers between inorganic particles and pol ymer matrix for toughening has been a controversial subject. In this resear ch, a series of rubber-encapsulated glass beads and its epoxy composites we re prepared, and underlying mechanisms which can connect material parameter s related with rubber interlayers with energy dissipation mechanisms, were investigated. The critical stress intensity factor (K-IC) and critical stra in energy release rate (G(IC)) of rubber-encapsulated glass bead filled epo xies were found to insignificantly depend on the existence and thickness of rubber interlayers. Microscopy studies on fracture process identified four different micro-mechanical deformations which can dissipate fracture energ y: step formation, micro-shear banding, debonding of glass beads, and diffu se matrix shear yielding. It was found that the first two became less exten sive and the others became more extensive as the thickness of rubber interl ayers increases. This offsetting effect of micro-mechanical deformations se ems to be the reason for the absence of significant toughening effect of ru bber interlayers. (C) 2001 Kluwer Academic Publishers.