Rolling contact fatigue behaviour of rails: Wedge model predictions in T-Gamma world

Abstract

In this study, T-Gamma and Wedge models have been compared with each other for the prediction of surface-initiated rolling contact fatigue cracks on rail surfaces. Both models are able to account for different observed rolling contact fatigue-wear regimes in tracks, but with very different physical backgrounds. The T-Gamma model uses empirically determined damage functions by introducing a relationship between the wear number (T-Gamma) and the rolling contact fatigue damage increment. Different rolling contact fatigue-wear regimes are considered in this empirical approach based on the idea that initiated cracks get partially or fully removed by the wear mechanism, not accounting for the full complexity of the occurring tribological phenomena. The Wedge model represents a physical approach, where contact stresses and its impact on plastic deformations and related material anisotropy are considered. Thus, the prediction of different rolling contact fatigue-wear regimes is based on these physical relationships, where plastic shear deformations in the near-surface layer play a key role. For comparison, the wheel–rail contact data from stochastic multibody dynamics simulations of a metro vehicle with conventional bogie technology running in three curve radii have been used. While the T-Gamma model always predicts the same rolling contact fatigue damage increment for a given T-Gamma value, the Wedge model shows a scattering of the predicted rolling contact fatigue damage increments when plotting them over T-Gamma because of the explicit consideration of contact stresses. Thus, each scenario consisting, for example, of certain vehicles, curve radius, wheel–rail profile combination, friction conditions, rail material, etc. needs its own damage function in the T-Gamma world. This should be kept in mind when applying the standard T-Gamma model to scenarios which differ significantly from the scenario it has been parameterised for.

Rail RCF damage quantification and comparison for different damage models

“…However, the treatment of results coming from MBS varies significantly amongst the approaches when it comes to quantifying RCF initiation in the wheel-rail contact. For instance, as Six et al [2] pointed out in their work, some models take into account loads/stresses only without consideration of wear, which continuously removes the material from the rail surface while some also take wear into account. However, at the end, they should predict the same results and agree with field observations.…”

Track Deterioration Model—State of the Art and Research Potentials

“…Investigations of alternative models that incorporate traction to assess rolling contact fatigue (RCF) and wear, such as those proposed by Six et al [64], may offer improvements in combined damage assessment.…”

“…As mentioned above, investigating alternative combined damage assessment models [64] that include traction may be a way to assess more aspects of rail damage in one model. This would have the advantage that the same damage model could be used, regardless of the wheelset type (driven or free rolling) and the alignment (straight or curved).…”