Simulation and validation of the ratcheting effects in B320 and R260MN rails under cyclic wheel–rail contacts

Abstract

The persistent head check (HC) damage in modern railways, a typical form of rolling contact fatigue (RCF), is primarily due to the ratcheting effects in rail. This study employed an efficient and accurate finite element (FE) wheel–rail frictional rolling contact model to simulate the ratcheting effects in rail steels (bainitic B320 and pearlitic R260MN) under 100 cycles of contact loading measured from the HC tests on V-Track test rig. The FE simulation considered both the rail material ratcheting (an intrinsic material property of steel) and structural ratcheting (subjected to altering cyclic contact loading conditions), with the former represented by a calibrated Chaboche constitutive model and the latter captured by the evolving contact patch in the FE simulation. The simulation results were then validated by comparing to the measured running-band width and rail head plastic deformation in the V-Track. A comprehensive analysis of the simulated and measured ratcheting effects confirmed that the bainitic B320 rail exhibited, under the same conditions considered, better anti-RCF performances in terms of slower accumulation of plastic deformation, smaller expansion of the contact patch, and subdued ratcheting rates compared to the R260MN rail. The study also revealed that rail structural ratcheting suppresses the material ratcheting around the longitudinal centreline of the contact patch under the cyclic wheel loading, while at the other locations within the contact patch, the structural ratcheting may intensify the material ratcheting at early cycles, and then suppress it when the contact stresses reach the level of those at the centreline. The ratcheting effects thus showed different patterns to the cases considering material ratcheting alone. Furthermore, the study confirmed that accumulation in residual stresses outside the contact patch can lead to accumulation in plastic strains beyond the rail running band, as the secondary effect of wheel–rail contact.