MICROMECHANICAL ANALYSIS OF DAMAGE MECHANISMS IN CERAMIC-MATRIX COMPOSITES DURING MECHANICAL AND THERMAL CYCLING
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This work presents a micromechanical study of the cyclic response of a undirectionally reinforced ceramic-matrix composite under time-varying load, parallel to fibres, and under thermal cycling. The analysis was based on the finite element method. The overall response was deduced from the response of a representative volume element consisting of concentrically placed cylinders of fibre and surrounding matrix, bounded axially by a matrix crack and a symmetry plane. The interface between the fibre and the matrix was assumed to be a frictional sliding contact (Coulomb friction). The results of this study indicated that the interfacial sliding stress s may be assumed to be constant over the sliding distance, whereas its variation with the remote applied stress is important. It was also found that the overall stress/strain behaviour is non-linear when the state of interfacial sliding is changing, while a linear response results for a fully sliding interface. In the latter case, the tangential modulus in loading differs from that in unloading. For thermal cycling, the analysis showed that, due to insignificant interfacial sliding, the thermal expansion coefficients in the damaged state are practically the same as in the undamaged state. 1993.