An experimental investigation of transient traction characteristics in rolling–sliding wheel/rail contacts under dry–wet conditions

This paper focuses on the effect of the boundary lubrication of water on the transient traction characteristics of two rollers contact. The traction coefficient was measured under wet condition using a twin-disc-type of rolling–sliding frictional machine, which can simulate the actual wheel/rail contact condition under a low slip ratio and low rolling speed. The experimental results of the transient traction coefficient curve against the sliding distance or running time under the wet condition are compared with the results under the dry condition in the previous paper [K.-S. Baek, K. Kyogoku, T. Nakahara, An experimental study of transient adhesion characteristics between rail and wheel under low slip and low velocity, Proceedings of the 7th Int. Conf. on Contact Mechanics and Wear of Rail/Wheel Systems (CM2006), Brisbane, Australia, 2006, pp. 341–349] for various parameters such as rolling speed, contact pressure, and slip ratio. The roughness and hardness of the contact surface are also measured at several sliding distances under the wet condition and the results show less variation in the roughness and hardness than those under the dry condition reported in the previous paper [1]. In addition, the difference between the new and worn test surfaces was investigated with an interruption in the test in order to observe the traction coefficient curve at the initial stage.