CREEP CRACK-GROWTH WITH SMALL-SCALE BRIDGING IN CERAMIC-MATRIX COMPOSITES

Time-dependent crack growth in ceramic matrix composites with linearly creeping fibers in an elastic matrix is predicted for bridged regions that are much smaller than the crack length. The relationship between crack openings and bridging tractions was modeled previously and acco unts for the mechanics of fiber pull-out while fibers are creeping. Th e length of the bridged zone is determined by a fiber failure criterio n and the condition that the stress intensity factor at the crack tip equals the matrix toughness. Solutions that relate constant crack velo cities to applied stress intensity factors are presented. Two fiber fa ilure criteria are considered: a critical crack opening and a critical total strain in the fiber at the crack plane. When fiber failure is g overned by a critical crack opening, bridging lengths will decrease wi th increasing velocity. For the case of a critical strain, the steady- state bridge length will increase with increasing velocity. Asymptotic analytical solutions are presented for cases where the crack velocity is small. (C) 1997 Acta Merallurgica Inc.