Direct measurement of crack-bridging tractions: A new approach to the fracture behaviour of ceramic/ceramic composites

By comparison with bulk ceramics, ceramic-matrix composites exhibit large toughening as a consequence, initially, of matrix crack bridging by intact fibres and then by broken fibres undergoing pull-our. A method for the direct measurement in double-edge-notched specimens of the bridging tractions, p, as a function of crack opening displacement, u, is presented. The p(u) curve shows a peak which corresponds to instability of the bundle of bridging fibres. The rail of the curve is linked to the fibre pull-out process and gives access-to the average pull-out length and to the interfacial sliding strength. Finally, the crack-growth resistance induced by the bridging phenomenon can be estimated from the integral of the p(u) curve. Two materials are used in this study: a woven 2D SiC/SiC composite processed by SEP, France, and a laminated [0/90] SiC/MAS-L composite processed by Aerospatiale, France. Results of p(u) curve analysis are given and discussed. (C) 1996 Elsevier Science Limited