Rail-wheel contact research at the University of Newcastle

This paper presents a review of state-of-the-art research on rail-wheel contact at the University of Newcastle, UK. The research centres on rail wear and rolling contact fatigue, integrating these processes and their interactions to model the entire life of the rail from installation to final failure. Also included are processes that determine the life, such as railwheel adhesion and lubrication. Better understanding of these processes and the factors affecting them will lead to solutions, such as improved coatings, or predictive tools to assist maintenance of the railways, ultimately reducing costs and increasing capacity. Wear and crack initiation. Wear and crack initiation are modelled as a ratchetting (accumulation of plastic deformation) process taking place over thousands of contact cycles. Material which accumulates an experimentally determined critical strain is defined to have failed. Where this occurs at the rail surface material may be removed as wear debris, and good correlation of the predicted wear rates with field tests has been found. Failed material deeper inside the rail cannot break away and is therefore taken to represent a crack, providing a quantified assessment of crack initiation. Rolling contact fatigue crack growth. Recent work in crack growth modelling has combined rail-wheel contact stresses with residual stress, continuously welded rail stress, and the possibility of wheel contacts running either side of the crack as well as directly across it. This has generated greater understanding of the factors which may cause a crack to turn up towards to the rail head, or down into the rail. Modelling contacts which are offset from existing cracks shows that growth rates can be slowed dramatically by just a few millimetres change in contact position, offering the possibility of new ways of planning grinding and maintenance strategies. Rail bending and multiple cracks. As cracks grow longer they begin to be driven by bending of the rail under the action of multiple train wheels, in addition to contact stresses. If multiple cracks are present they interact, and results from multi-crack models of the rail in bending are significantly different from those of single crack models. Low-adhesion leaf films. The rail-wheel interface friction level is crucial for safety and timekeeping, particularly if it is too low. Recent work will be presented on the investigation of low-adhesion leaf films that form during the autumn. Coatings. The application of coatings to the regions of the rail under greatest stress offers new possibilities for wear and rolling contact fatigue life extension. Investigations have been conducted to examine wear and rolling contact fatigue of coated rails, indicating real possibilities for rail life extension.