Wheel/rail adhesion and damage under different contact conditions and application parameters of friction modifier

Friction modifier (FM) is a newly developed third medium to control the service performance of wheel/rail. The wheel/rail performance is influenced by the wheel/rail contact conditions and FM application parameters. Therefore, the effects of FM application parameter and the wheel/rail contact parameters on the adhesion and damage behaviors of wheel and rail materials should be explored. In this study, the influences of application amount of FM, the wheel/rail contact stress and the creepage on the adhesion and damage behaviors were studied using a twin-disc machine. Results indicated that the increase in contact stress would reduce the wheel/ rail minimum adhesion coefficient and effective holding time of FM. The increase in the creepage would increase the adhesion coefficient and reduce the holding time. Under the wheel/rail contact stresses of 800 and 1100 MPa, the application of FM could reduce wheel/rail wear and damage. But under 1500 MPa, FM could cause serious rail surface damages. Moreover, the surface crack propagation process of rail mainly included three stages: initial stage, transition stage and rapid propagation stage. The "oil wedge effect" was the main mechanism for aggravating the surface damages of rail under 1500 MPa.