Finite element method simulation of transverse bridging in fiber reinforced composites

Abstract

Delamination cracks in ceramic composite materials may be bridged by misaligned or inclined fibers at a shallow angle. The in situ observation of delamination cracks in a Si-Ti-C-O fiber-bonded ceramic composite material reveals that the bridging fibers are subjected to increasing tensile stresses as the crack opening displacement becomes larger. These stresses cause a crack closure pressure that is considered to contribute to steady state transverse fracture toughness. To relate the crack closure pressure to the material properties of fibers, matrix and their interface, a two-dimensional FEM model of a misaligned fiber bridging the crack wake at a shallow angle was constructed. Crucial mechanisms such as fiber debonding and frictional sliding along the debonded interface as well as matrix chipping were included. The crack closure pressure was simulated as a function of COD and the influences of these mechanisms were discussed. The toughening effect of bridging fibers was estimated and the obtained results were compared to the experimental data for a Si-Ti-C-O fiber-bonded ceramic composite material.