ABSTRACT
This chapter discusses the mechanisms for achieving toughening in a ceramic material. It also reviews progress with the application of these mechanisms to specific ceramic materials. Fiber length also affects the toughening and strengthening capability of fibers in a composite. Additional major effort has been directed toward improving reliability by increasing the fracture toughness of ceramics to inhibit crack propagation. Substantial progress has been achieved with approaches such as self-reinforced microstructures, particle dispersions, whisker dispersions, transformation toughening, long-fiber reinforcement, ductile phase reinforcement, and prestressing. Ceramics generally fracture in tension, i.e., in a crack-opening stress mode. Prestressing involves placing a portion of the ceramic under a residual compressive stress. Crack shielding is a stress-induced microstructural change that results in a reduction in stress at the crack tip. The effect occurs in a zone around the crack tip and extending back along the crack.
