Keywords: wear, wheel-rail contact.

Modelling to predict the evolution of rail (and wheel) profiles using design tools that integrate multi-body dynamics simulations of track and rail vehicles with tribological models of material removal are well established. Two approaches are typically used for modelling the wear processes, both semi-empirical. The first utilises the Archard adhesive wear equation and the second relates material loss to energy in the contact calculated as the Tgamma number. Both rely on establishing wear coefficients using sliding or rolling/sliding wear experiments. The Tgamma approach is currently used extensively in the United Kingdom by, for example, Network Rail in the "Whole Life Rail Model" where it is also used as an indicator of rolling contact fatigue (RCF).

However, all wear coefficients used currently were generated using dry contact conditions and cannot take account of contaminants present on the rail, either naturally, such as water from rain, dew, leaves etc. or those applied to manage friction, such as lubricants, friction modifiers (liquid or solid) or traction enhancers (sand or particles suspended in a gel). One way that is used to overcome this problem is to change the friction coefficient used as an input to the multi-body dynamics modelling to one representative of the contaminated conditions being experienced. This may help in terms of the dynamic modelling, but for the wear it simply serves to move to a different point on the dry wear curve, whereas in fact with a contaminant present a new wear curve is required as the contaminant will change the wear mechanisms prevalent and affect how the energy in the contact is dissipated.

Another serious limitation of the multi-body dynamics solutions used is that friction, being an input is fixed even as the slip within the contact varies. Friction, however, is actually a result of the contact conditions experienced and varies constantly as slip varies (see any typical creep curve).

In this paper experimental data derived from twin disc testing is used to illustrate how wear and friction changes when substances such as water and grease present in the contact. Contact modelling using Fastsim is also used to highlight the differences apparent in forces and wear amounts when using full creep curves and more representative wear coefficients.

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