FINITE-ELEMENT METHOD SIMULATION OF TRANSVERSE BRIDGING IN FIBER-REINFORCED COMPOSITES

Delamination cracks in ceramic composite materials may be bridged by m isaligned or inclined fibers at a shallow angle. The in situ observati on of delamination cracks in a Si-Ti-C-O fiber-bonded ceramic composit e material reveals that the bridging fibers are subjected to increasin g tensile stresses as the crack opening displacement becomes larger. T hese stresses cause a crack closure pressure that is considered to con tribute to steady state transverse fracture toughness. To relate the c rack closure pressure to the material properties of fibers, matrix and their interface, a two-dimensional FEM model of a misaligned fiber br idging the crack wake at a shallow angle was constructed. Crucial mech anisms such as fiber debonding and frictional sliding along the debond ed interface as well as matrix chipping were included. The crack closu re pressure was simulated as a function of COD and the influences of t hese mechanisms were discussed. The toughening effect of bridging fibe rs was estimated and the obtained results were compared to the experim ental data for a Si-Ti-C-O fiber-bonded ceramic composite material.