Fracture in angle-ply ceramic matrix composites

An analytical/computational fracture mechanics scheme, combined with finite element computations, is presented to explain observed fracture patterns in angle ply fiber-reinforced ceramic composite laminates. Unlike polymeric composites, where microcracks are channeled parallel to the fiber directions, cracks in ceramic composites initiate perpendicularly to the load axis. The results presented herein provide rational explanations for the experimental observations and confirm the advantages bestowed by multi-directional reinforcements. Such reinforcements would still allow the development of multitudes of matrix cracks, bridged by intact fibers, that lead to the desirable gradual and `graceful' failure of the composite. At the same time, multidirectional reinforcement prevents premature failures by constraining the laminate against interfacial fiber/matrix debondings. Such debondings, which may otherwise grow rapidly along the abovementioned weak interfaces, may readily occur in unidirectionally reinforced off-axis laminates, as noted in a preceding article.