R-CURVE AND COMPLIANCE CHANGE UPON RENOTCHING

A novel approach is addressed in the application of the renotching technique to the consideration of toughening processes and mechanisms of ceramic materials. Crack-bridging stresses and the contribution of other mechanisms which enhance crack-face friction are stepwise removed during renotching. This technique enables one to determine the amount and distribution of bridging stresses behind the crack tip, as well as to separate the contributions of crack-face, crack-wake, and crack-tip processes and mechanisms. Five ceramic materials with different microstructures are used for experimentally determining their conventional K(R)- and ''renotched'' K(R)-curves in addition to measuring the compliance changes during extending as well as renotching the crack. A simple theoretical approach is presented and applied to the experimental results, which enables one to easily determine the magnitude and the distribution of crack-face bridging stresses. The contributions of various toughening processes to the conventional and the renotched R-curve behavior are discussed.