MATRIX CRACKING IN UNIDIRECTIONAL CERAMIC MATRIX COMPOSITES UNDER QUASI-STATIC AND CYCLIC LOADING

Experimental data associated with the development of matrix cracks in unidirectional continuous silicon carbide fibre/calcium alumino-silicate matrix laminates under quasi-static loading are presented, including crack density, residual strain and hysteresis behaviour as functions of applied stress. Simple models are developed, based on an assumption of purely frictional load transfer between the fibre and matrix, which describe reasonably well the quasi-static stress-strain behaviour in the presence of cracks. Under tension-tension mechanical fatigue cycling it is found that the crack density stabilises at a relatively early stage in the test. Based on the quasi-static model, the changes in fatigue hysteresis loops on fatigue cycling are interpreted in terms of a reduction in the effective frictional interfacial shear stress.