Influence of rail, wheel and track geometries on wheel and rail degradation

Doctoral thesis, 2015

For more efficient railway maintenance there is a need to increase the understanding of the influence of operational conditions on wheel and rail degradation. To this end, the chosen primary investigation strategy is to employ dynamic multibody simulations, where operational conditions are altered, to estimate the influence on material deterioration. Operational conditions considered are track, wheel and rail geometries; and types of material deterioration that are considered are rolling contact fatigue (RCF) and wear. Track geometry, especially the curve radius, has a large influence on wheel/rail degradation. Smaller curve radii lead to higher degradation. By also considering the influence of lateral track irregularities in curves, a more complicated relationship emerge. Large curve radii and a high level of lateral irregularities lead to an increase in RCF over the length of a curve. For small radius curves, where wear is the dominating damage mechanism, an increase in the level of lateral irregularities leads to a transition towards a mixed RCF/wear regime for the outer (high) rail. The influence of wheel and rail geometries on degradation is studied by parametrisation of wheel/rail geometries, employing a design of experiments scheme to the multibody simulations that determine degradation, and finally by deriving meta-models through regression analysis. The meta-models link estimated degradation magnitudes to key geometric parameters. The advantage of the meta-models is that degradation magnitudes can be evaluated with a very low computational cost. This has the benefit that measured wheel and rail profiles can be ranked based on how detrimental they are. Examples are presented for altered gauge corner and flange root geometries, and also for hollow worn wheels. A field study of RCF of locomotive wheels shows its strong dependence on operational conditions. Seasonal variations in the number of wheel reprofilings are explained in terms of seasonal variations in weather conditions, lubrication practices and rail grinding.