Fracture Behaviour of Epoxy Resins Modified with Liquid Rubber and Crosslinked Rubber Particles under Mode I Loading

Three-point bending tests were conducted with two kinds of rubber-modified epoxy resins: a liquid rubber-modified epoxy resin and a nano-elastomer particle-modified one. In most studies on rubber-toughened epoxy resins, fracture toughness has been evaluated by critical stress intensity factor or critical energy release rate, where the crack is assumed to propagate rapidly, and stable crack propagation has not been considered. However, stable crack propagation was observed for the present rubber-modified epoxy resins. To take into account crack propagation, fracture toughness was characterized using the crack-growth resistance curves (R-curve). In the present study, the evolution behaviour of the damage zone near the crack tip was observed using a video-microscope for the two kinds of rubber-modified resins. Furthermore, to investigate microscopic fracture mechanisms, the fracture surfaces were observed by scanning electron microscopy, and side views near the crack tip were also observed by a confocal laser scanning microscopy.