Fatigue Behavior of Alumina with Surface Crack. Effects of Initial Surface Crack Size and Multiple Surface Cracks.

Abstract

In this paper, the effect of crack size, number and distance between the centers of surface cracks on the fatigue behavior of alumina has been investigated. A single crack and two or three collinear surface cracks were introduced by Vickers indenter. The crack size was changed by several indentation load. The fatigue tests were carried out under static tensile loading (stress ratio R=1) and cyclic loading (R=0 and -1). The main results were as follows. ( 1 ) For any surface crack size, appreciable decrease in fatigue lifetime due to cyclic load was observed, and the degree of the decrease was almost the same for each crack size. ( 2 ) No appreciable effect of stress ratio was observed in the decrease in fatigue lifetime due to cyclic loading. ( 3 ) An interaction of multiple surface cracks, that is to say, the decreasing fatigue lifetime by the interaction with the increase in the nurnber of crack or the decrease of the distance between those cracks was more clearly observed in the case of small crack size, while no interaction was observed In the case of large crack. Such a result seems to be caused by the reason that the interaction of multiple surface cracks may be cancelled by the higher crack propagation resistance owing to bridging effect in crack tip.