Initiation and Propagation of Fretting Fatigue Crack in the Very Long Fatigue Life

In fretting fatigue, a fatigue crack initiated from the contact edge can be found even in the specimen which survives up to 107 cycles. This fact means that fretting fatigue fracture may occur if the specimen undergoes very long fatigue cycles (more than 107 cycles). To characterize the fatigue properties of very long life fretting fatigue, it is necessary to understand the effect of the singular stress field near the contact edge on the crack initiation and propagation. In this study, fretting fatigue tests below the fatigue limit (corresponding to 107 cycles) were carried out. The fatigue tests were interrupted at 107 cycles, and the fatigue cracks were observed by SEM. Numerical analysis by FEM was also carried out. It was found that the fatigue crack initiation at the contact edge could be evaluated by the stress intensity coefficient of the singular field, and the crack propagation/non-propagation could be estimated. by ΔKθmax in the direction of Δσθmax, with an introduction of an initial crack with the critical length over which the linear fracture mechanics can be applied.