The influence of the interphase and associated interfaces on the deflection of matrix cracks in ceramic matrix composites

A model is proposed to determine the influence of an interphase on the defl ection of a matrix crack in ceramic matrix composites. Then, a finite eleme nt analysis is performed for a microcomposite geometry with an annular crac k which initiates in the matrix and propagates in the interphase. It is app lied to a SiC/C/SiC microcomposite with a pyrocarbon interphase. Criteria f or penetration and deflection of the matrix crack are expressed in terms of toughness of the interphase and of the various interfaces (matrix/interpha se and interphase/fibre interfaces). The predictions are found to agree wit h crack deflections observed in practical SiC/SiC composites and with the a vailable interphase toughness data. Results also suggest that the real crac k deflection mechanism involves debonding ahead of the propagating matrix c rack. (C) 2000 Elsevier Science Ltd. All rights reserved.