Rail rolling contact fatigue formation and evolution with surface defects

Surface defects can induce serious rolling contact fatigue (RCF) damage at wheel/rail interfaces and even cause fracture failure of rail material. This study aims to explore the formation mechanism of surface defects on rails, and to trace the evolution process of RCF behavior of material around the surface defect. Experimental studies were conducted on a wheel/rail twin-disc machine considering two forms of defects: indentation defects caused by ballast impacts (IDBs) and indentation defects caused by cone penetration head impacts (IDCs). Results indicate that IDB can cause RCF cracks that propagate downward deep into the subsurface of rail due to the formation of a material hardening layer (MHL), causing severe damage. IDCs with different sizes and angles were grouped into an affected group and a non-affected group by considering a critical size dividing line and whether the MHLs existed on the defect surface or not. The evolution process of a crack in the affected group includes four main periods: fracture of the MHL, crack initiation, the rail steel matrix filling up the MHL gap and crack propagation downward. Further, the increase in both the angle and the depth of the IDC would lead to severe RCF damage.