Effect of contact conditions on growth of small crack in fretting fatigue

As the general features of fretting fatigue, initiation of fretting fatigue crack is in the very early stage of the fretting fatigue life and there are small non-propagating cracks in the test specimen that doesn't fracture at the fretting fatigue limit. In accordance with these experimental facts, fretting fatigue problem can be considered as a propagation problem of small crack. Thus, a pre-cracked specimen was used in the fretting fatigue test in this study. The objective was to consider the determinant factors of fretting fatigue strength. In the fretting fatigue test, the fretting fatigue limit of the pre-cracked specimen was once reduced and after increased with increase of the contact pressure. The reason was understood by the stress intensity factor of the pre-crack obtained by a finite element analysis. In this study, the fretting fatigue limit can be predicted by the comparison of ΔK of the pre-crack and the propagation threshold of the pre-crack ΔKth. The effect of the relative location of the pre-crack to the contact edge on the fretting fatigue strength was also discussed by both fretting fatigue test and FEM analysis.