Abstract
In order to investigate the effects of grain bridging degradation on the cyclic in polycrystalline alumina, crack propagation tests were carried out under cyclic load and static load. Two kinds of small semi-elliptical surface crack were introduced by Knoop indenter. Polishing the surface layer, the residual stress around the Knoop indentation was completely removed. The cyclic loading accelerates crack propagation in small crack as the same as in long crack. On the other hand, measuring and analyzing the crack opening displacement (COD) of 350μm crack, we determined the net stress intensity factor KItip. Under the cyclic load, the reduction of bridging force resulted in an increase in KItip which, in turn, accelerated the crack propagation rate. Furthermore, it is found that bridging degradation mechanism under cyclic loading does occur, but that this mechanism is not sufficient to completely account for fatigue crack growth in ceramics.
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