Experimental and numerical study on the multi-site fretting fatigue crack initiation of press-fitted axles

In this study, fretting fatigue tests were conducted to gather information on both fretting fatigue and fretting wear. Subsequently, an evaluation methodology that combined the Modified Wohler Curve Method (MWCM) with the theory of critical distance (TCD) was established to investigate multi-site fretting crack initiation. The results showed that the fretting fatigue damage could be reasonably evaluated using the MWCM equivalent stress sigma MWCM. sigma MWCM is greatly influenced by both bulk stress and fretting wear-induced stress concentration. The stress field close to the wear boundary increased due to the continuous fretting wear, leading to an increase in sigma MWCM; meanwhile, the bulk stress near the wear boundary decreased as the crack propagated, resulting in a decrease in sigma MWCM. The combined effect of the fretting crack propagation and wear caused sigma MWCM, which was located within an annular strip of the axle, to exceed the critical value, causing the multi-site fretting crack initiation. The fretting fatigue strength corresponding to 107 test cycles was measured using the staircase test.Experimental results indicated the absence of a conventional fatigue limit for fretting fatigue.A parameter for describing the local stress that controls fretting fatigue damage was determined.The mechanism of multi-site fretting crack initiation in press-fitted axles was clarified.