CRACK-BRIDGING ANALYSIS FOR ALUMINA CERAMICS UNDER MONOTONIC AND CYCLIC LOADING

Frictional degradation of grain-localized bridges behind a crack tip has been recognized as the major cyclic fatigue mechanism in alumina ceramics. Such a fatigue mechanism implies that the crack growth resistance (R) curve behavior during cyclic fatigue is different from that of monotonic loading due to the reduction in crack-tip shielding. A recent crack-bridging theory based on crack compliances is used to study the bridging stresses under monotonic loading and during cyclic fatigue. The bridging-stress distributions of two coarse-grained aluminas under monotonic loading are determined using compliance measurements. Because the interlocking grain bridges at the crack wake are subject to frictional damage from cyclic loading, the bridging-stress distribution evaluated during cyclic fatigue is distinct from that for monotonic loading. These results indicate that it is incorrect to incorporate the R-curve behavior from monotonic loading to the analysis of cyclic fatigue of alumina ceramics.