Analysis of crack deviation in ceramic matrix composites and multilayers based on the Cook and Gordon mechanism

In ceramic matrix composites, cracks that initiate in the matrix may be deflected in the fibre/matrix region, depending on interface characteristics. The most recent CMCs possess multilayered matrices and interphases. Cracks can be deflected within the layers or along interfaces depending on layer bonding.In this paper, the extension/deflection of a crack located in the vicinity of an interface is examined. All situations, including multilayers, interphases, etc. are covered by a single elementary cell made of two materials, one of which is cracked. A crack deflection condition is proposed. The model is based on the Cook and Gordon mechanism which considers debonding ahead of the crack tip as a result of the multiaxial stress state induced by the crack. Finally, the model is applied to various fibre/matrix combinations involving carbon or silicon carbide, and pyrocarbon or boron nitride based interphases.