Effects of crack—fiber interactions on crack growth rate in fiber-reinforced brittle matrix composite under cyclic loading: model experiment

The crack—fiber interaction process and measurement of the crack growth rate of a fiber-reinforced brittle matrix composite have been studied using a single SiC fiber-reinforced polymethyl methacrylate (PMMA) model composite. The change in interfacial shear sliding stress due to cyclic loading—unloading was obtained by a thin specimen push-back test. The interfacial shear sliding stress decreased slightly after cyclic loading and this behaviour originated from wear of the sliding interface. The crack growth rate of the composite, da/dN, vs. crack length relation was strongly affected by the interaction process. Elastic constraint before interface partial symmetrical debonding and crack bowing after this debonding were the major sources of da/dN reduction of the composite. After the matrix crack surrounded the fiber, da/dN was slowed by the crack-shielding mechanism originating from fiber bridging. This process continued throughout the tested number of applied cycles, because the interfacial shear sliding stress transfer operated during cyclic loading. The three-dimensional crack—fiber interaction process during crack propagation and its effects on da/dN under cyclic loading in a fiber-reinforced brittle matrix composite were discussed.