Creep damage in SiC/SiC composites

In SiC/SiC composites, the matrix has greater creep resistance than the fibers. The consequent fiber deformation has been shown to transfer sufficient stress onto the matrix that, above a threshold, matrix cracks propagate across the 0(0) plies. This process increases the compliance of the composite and reloads the fibers, resulting in creep rates dominated by the fibers. The extent of the compliance change is limited by the high temperature interface friction stress tau, through its effect on the crack density. After creep, tau is diminished substantially from its room-temperature magnitude, resulting in low crack densities and extensive fiber pull-out. A matrix-cracking solution for composites with creeping fibers has been used to correlate the experimentally determined rates of compliance change and the creep strain.