Transitions in rolling-sliding wheel/rail contact condition during running-in

The risk of wheel-climb derailment increases if the traction coefficient in the wheel/rail contact is too high. This has been observed to happen more frequently just after wheel machining. This work investigates how the traction coefficient rises with evolution of the wheel/rail interface during the running-in. Experiments were performed using a full-scale wheel/rail contact rig and an ultrasonic array transducer mounted in the rail. Results were used to determine the stiffness of the contact interface. Contact stiffness appeared to be positively correlated with the traction coefficient. Owing to the conforming of the interface, contact stiffness increases before the traction coefficient rises. The work will allow recommendation of wheel machining to be made to help reduce the problem of wheel-climb derailment.