Fatigue degradation of the crack wake zone in monolithic alumina

This study examines the microstructural role of crack-face bridging mechanisms in a monolithic ceramic, subjected to cyclic loading conditions. By utilizing a unique post-fracture-tensile experiment, the fatigue properties of a commercially available alumina are examined. Based on the current results, one will conclude that a frictional wear mechanism is activated when the crack-bridging grains are permitted to slide in their sockets. When the peak 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 effectiveness of the bridging stress and lowers the toughness of the material. For the 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 Metallurgica Inc. Published by Elsevier Science Ltd. All lights reserved.