Fatigue degradation of the crack wake zone in monolithic alumina

This study examines the microstructural role of crack-face bridging mechani sms in a monolithic ceramic, subjected to cyclic loading conditions. By uti lizing a unique post-fracture-tensile experiment, the fatigue properties of a commercially available alumina are examined. Based on the current result s, one will conclude that a frictional wear mechanism is activated when the crack-bridging grains are permitted to slide in their sockets. When the pe ak loads and displacements are held below values which cause grain sliding, no fatigue damage is evident. Above the threshold values, however, notable damage may be observed. This cumulative wear process reduces the effective ness of the bridging stress and lowers the toughness of the material. For t he quasistatic bridging problem, accumulation of damage has been related to grain-size features, but apparent from data in this study, fatigue-related damage depends upon damage to sub-grain-size features. (C) 1999 Acta Metal lurgica Inc. Published by Elsevier Science Ltd. All lights reserved.