Friction and wear behaviour of rolling–sliding steel contacts

Improving the total life cycle costs and safety of trains are current research topics that hold great interest for those who build, maintain and operate trains. The maintenance interval for both wheels and rails has become a major issue in reducing costs and increasing safety and has encouraged the development of new tools for predicting the evolution of wear in order to establish a convenient maintenance schedule. These new tools require the synergy of dynamic analysis and the development of suitable wear models. Rail/wheel wear depends on the material properties resulting from a competition between contact fatigue and sliding wear. Therefore, all the contact conditions affecting the contact stress distribution will determine the wear behaviour. The current research paper investigates the effect of contact conditions on friction and wear behaviour of carbon and low alloy rail/wheel steels. Two-disc rolling-sliding tests were done to study the effect of the creep ratio, contact pressure and tangential speed on the resulting traction coefficient and amount of wear. Scanning and optical microscopy and the evolution of micro hardness were used to observe crack growth beneath the contact surface and to evaluate the strain-hardening effect, induced by contact stresses. Further rolling-sliding and unidirectional sliding tests were performed to assess the wear of the wheel rims. Results were analysed and discussed, comparing the effectiveness of a classical approach based on Archardʹs equation, with models involving the energy dissipated by friction.