Open System Tribology in the Wheel–Rail Contact—A Literature Review

The tiny contact zone (approximately 1 cm²) where steel wheel meets steel rail is fundamental to rail transport. This work is a comprehensive presentation of recent research in wheel–rail contact tribology. It stresses that, unlike gears or rolling bearings which are sealed contacts with reduced exposure to the surrounding environment, a wheel–rail contact is an open system that is exposed to dirt and particles as well as to applied and natural lubrication (the latter category includes rain, dew, and biological materials such as leaves). As an open system contact, it also radiates sound and airborne wear particles. These characteristics of an open system underscore the need for special studies of open system tribology. Areas requiring study include airborne particle emissions and the environmental effects of applied lubrication and friction modification. Given that adhesion, wear, and sound and particle emission are closely related in an open system, these should be studied together rather than independently.