Evaluations of Early-Stage Fatigue of Tilted Pre-crack of Silicon Nitride Balls Under Cyclic Compressions: Comparisons Between 274 μm-Length and 469 μm-Length Cracks

The fatigue crack growth from the tilted pre-crack on the silicon nitride balls were analysed by using the maximum stress intensity factor and the crack extension. The pre-cracks were introduced with the Vickers indenter under the 10 kgf (shorter length) and 20 kgf (longer length) indentation force. The geometrical size of the fatigue crack in the case of the shorter pre-crack (10 kgf) was smaller than that of longer pre-crack (20 kgf). However, the maximum values of the initial stress intensity factors were the same in the present tests. The expansion rates of the shorter pre-crack (10 kgf) were lower than that of the longer pre-crack (20 kgf). And the more fatigue cycles were needed to reach a certain length in the case of the shorter pre-crack (10 kgf), compared to that of the longer pre-crack (20 kgf). These results indicate that the fatigue crack growth from the shorter pre-crack (10 kgf) was retarded than that from the longer pre-crack (20 kgf). It is concluded that the pre-crack lengths affected the fatigue crack growth behaviour as well as the maximum stress intensity factor.