Material defects in rolling contact fatigue — influence of overloads and defect clusters

The fatigue impact of material defects under rolling contact loading, with emphasis on wheel/rail contact, is studied. In particular, the response to overloads and the effect of clusters of defects are investigated. The study is carried out using numerical finite element (FE) simulations. Stresses and strains in the vicinity of the defects are analysed and the fatigue impact is quantified by means of a multiaxial fatigue criterion. It is found that overloads are detrimental, causing a permanent extension of the impacted zone surrounding a defect. Further, clustering of defects leads to a highly stressed zone between adjacent defects, through which a fatigue crack is likely to propagate. A combination of defect clusters and occasional overloads is found to be a plausible explanation to the initiation of deep subsurface fatigue cracks.