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 growt h rate of a fiber-reinforced brittle matrix composite have been studie d using a single SIC fiber-reinforced polymethyl methacrylate (PMMA) m odel composite. The change in interfacial shear sliding stress due to cyclic loading-unloading was obtained jy a thin specimen push-back tes t, The interfacial shear sliding stress decreased slightly after cycli c loading and this behaviour originated from wear of the sliding inter face. The crack growth rate of the composite, da/dN, vs. crack length relation was strongly affected by the interaction process. Elastic con straint before interface partial symmetrical debonding and crack bowin g after this debonding were the major sources of da/dN reduction of th e composite. After the matrix crack surrounded the fiber, da/dN was sl owed 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 durin g cyclic loading. The three-dimensional crack-fiber interaction proces s during crack propagation and its effects on da/dN under cyclic loadi ng in a fiber-reinforced brittle matrix composite were discussed.