Modelling rail wear transition and mechanism due to frictional heating

Wear rate in a rail–wheel system has been found to be a function of temperature rise between the rail and wheel. The flash temperature due to frictional heating causes the development of thermal stresses and reduction of the material strength at the rail undergoing wear. This thermal effect leads to a rapid increase in wear rate, known as wear transition. Rail wear transition behaviour as a result of frictional heating in the contact region has been investigated using a computer modelling technique and the results are presented here. The model is based on ratchetting failure, which is caused by the accumulation of plastic strain in the rail material over many cycles. Plastic strain causes the rail material to harden but as the temperature increases, thermal softening may occur, which can reduce the strength of the material. Above a certain temperature, both thermal stress and thermal softening can significantly influence the wear rate. The variations in the slip/roll ratio, the peak pressure, the friction coefficient, and the vehicle speed on the wear rate show that the transition from mild to severe wear occurs at temperatures above 350 °C. During this transition the vehicle speed has the least effect on the temperature and wear rate among the other parameters.