In the previous paper, experimental work was reported in which the crack generation during fretting in a vacuum was dependent on the slip amplitude and normal load. In this paper, the condition of the crack generation is considered. The tensile stress concentration at the trailing edge of the contact area depends on the tangential force coefficient and the contact pressure. The properties of the stress concentration against load and slip amplitude are very similar to those of the crack generation. The mechanism of crack initiation in low-cycle fatigue is applied to the crack generation in fretting; when the stress concentration causes local yielding at the edge, the accumulation of the local plastic strain occurs during the repetition of the fretting cycle, followed by the initiation of the crack. The reason why a crack is not generated during fretting in air is discussed.
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