Fretting fatigue strength and non-propagation of surface cracks

Components behaviour under alternate loads combined with repeated relative surface motion is one of the open problems in the area of fatigue. The combination of the effects of abrasive and adhesive wear, caused by relative surface sliding and resulting in surface damage, and fatigue, caused by alternated loads in presence of high local stress intensity factors (i.e surface degradation by wear), is called "fretting fatigue". A presence of oxidation phenomenon can also be part of the fretting fatigue process. In the case of the railway wheelsets designed after 2003, there are no records of failures at press-fits because the design rules are based on shape of the transitions (D/d ≥ 1.2) that make the axle transition the most stressed point. However, it is important to analyze the acceptability of defects and micro-cracks at the press-fits in order to correctly interpret fatigue strength considering that micro-scars and micro-cracks are some times detected after fatigue tests for D/d = 1.2. In this paper we analyse the full-scale test results obtained on EA4T axles within the Euraxles project on the basis of detailed FE analyses and a new criterion for prediction non-propagation of cracks under RCF conditions. Predictions are compared with full-scale test experiments on axles with artificial micro-notches at the press-fit.