CRACK-PROPAGATION BEHAVIOR IN ALUMINA CERAMIC UNDER STATIC AND CYCLICLOADING

Region 3 crack propagation under static loading is independent of the environment. This mechanical crack propagation curve can be expressed by the four-parameter Weibull function. On the other hand, Region 1 cr ack propagation is very sensitive to the humidity in the environment. This effect can be well explained by introducing the environmental fra cture toughness, K(Ie), into the Weibull function. From the numerical integration of the equations of these static crack growth curves, the cyclic fatigue cracking behavior can be predicted. The data for a lowe r range of the stress intensity factor, DELTAK, show the acceleration of cracking by cyclic loading. The rough specimen surface and the part ially fractured grain boundary near crack path, appearing only in cycl ic fatigue fracture, may explain this acceleration.