APPLICATION OF WEAKEST-LINK FRACTURE STATISTICS TO FIBER-REINFORCED CERAMIC-MATRIX COMPOSITES

The strength and reliability of fiber-reinforced ceramic-matrix compos ites (CMCs) are dependent on whether conditions of local or global loa d sharing prevail, Global load sharing is promoted by a low interfacia l sliding stress and is manifested in a zero-tangent modulus at the po int of tensile failure along with random fiber failures and extensive fiber pullout, In this paper, it is demonstrated that conditions of gl obal load sharing are not present in two commonly studied CMCs, despit e the fibrous appearance of their fracture surfaces, This behavior is manifested in a volume-dependent strength, as evidenced by strength di fferences measured in tension and flexure (accounting for the nonlinea r stress distribution in flexure), Methods of weakest-link statistics are used to relate the strengths measured in the two test configuratio ns, Estimates for the Weibull moduli of the two systems are obtained f rom the experiments and compared with values obtained through Monte Ca rlo simulations based on a three-dimensional-lattice Green's function method, The implications of these results on the strength of large com ponents and of small regions of high stress concentration are discusse d briefly.