Keywords: wheel-rail contact tribology, wear, rolling contact fatigue, adhesion, third body materials.

The wheel-rail contact is a crucial component in the successful operation of railways. Effective management of the contact is, therefore, a very important aspect of rail infrastructure operations. Rail maintenance within the European Union costs hundreds of millions of Euros, thus, gaining a good understanding of the contact and how it is affected by changing conditions, is critical to designing methods to optimise performance.

A large variety of loading conditions and contact geometries exist arising from the many different rail and wheel profiles, rail cant and curve radii, and railway vehicles running on a network. Contact conditions vary considerably, and friction and creepage in the contact are also highly variable.

The situation is further complicated by the presence of third body materials in the contact. These may be naturally occurring: such as humidity; precipitation; leaves; or products applied to the rail or wheel surface for a particular purpose, such as friction modifiers; greases; traction gels etc. A third body layer exists even with a dry, uncontaminated contact, which is made up of oxides and wear debris. All of these will have an influence on damage processes and adhesion.

All the influencing factors have to be taken into account as they interact closely. For example, measures used to reduce wear, such as lubrication, can influence fatigue and adhesion, and the measures used to increase adhesion, such as sanding, can have a detrimental effect on wear. A fine balance has to be found in determining maintenance schedules and lubrication regimes to keep railway networks running smoothly.

This paper outlines previous and current work carried out to experimentally characterise the tribology of the wheel-rail contact covering wear, rolling contact fatigue, adhesion and wheel-rail isolation (important to avoid to maintain train detection), and examine how they are affected by third body materials in the wheel-rail contact; both natural and applied. Consideration is also given to how these effects can be built into tribological models for prediction of wheel and rail life, and where data gaps exist.

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