抄録
From the fractographic observation on silicon nitride specimens failed under rolling contact fatigue, it has been found that the crack initiation in silicon nitride specimens subjected to rolling contact fatigue is induced by cyclic subsurface shearing stress, as is known in steel bearings. Though these subsurface cracks are produced in the direction parallel to the cyclic shearing stress, cracks grow in the direction near to the plane of the maximum tensile stress if mode II loading is applied to them. The difference between the crack growth in simple mode II loading and the crack growth in rolling contact fatigue is, we suppose, whether or not there is a superimposed compression stress. Based on this hypothesis, we developed an apparatus to obtain intrinsic mode II fatigue crack growth characteristics, as a simplified model of determining the subsurface crack growth in rolling contact fatigue. Some preliminary results on da/dN-ΔKII relations have been obtained by using this apparatus on a steel and aluminum alloys.
