This proposed program aims to study several classes of ceramics and ceramic matrix composites, representing materials with different mechanisms of toughening. The objective is to discover why and how fatigue cracks grow in monolithic ceramics where toughening is induced by crack deflection and/or grain bridging, such as in coarse and fine grained Al2O3 and grain-elongated Si3N4. Other materials include the transformation and microcrack toughened ceramics such as PSZ and ZTA, the brittle fiber or whisker reinforced ceramic matrix composites such as SiC-whisker reinforced alumina, and the ductile-phase toughened ceramic matrix composites such as Al-toughened alumina. Fatigue tests, together with microstructural characterization of the degradation of the crack-tip shielding (toughening) mechanisms behind the crack tip and accumulated microstructural damage ahead of the tip, will be used to study the micromechanism of cyclic crack-growth in these materials. %%%% This research is designed to seek a fundamental understanding of the mechanisms by which ceramics suffer cyclic fatigue failure. A number of ceramic materials, representing materials with different mechanisms of toughening, will be used for this study. Microstructural characterizations together with fatigue tests are used to study the micromechanisms of cyclic crack-growth in these materials.
