An experimental study on the effects of friction modifiers on wheel-rail dynamic interactions with various angles of attack

By modifying friction to the desired level, the application of friction modifiers (FMs) has been considered as a promising emerging tool in the railway engineering for increasing braking/traction force in poor adhesion conditions and mitigating wheel/rail interface deterioration, energy consumption, vibration and noise. Understanding the effectiveness of FMs in wheel-rail dynamic interactions is crucial to their proper applications in practice, which has, however, not been well explained. This study experimentally investigates the effects of two types of top-of-rail FM, i.e. FM-A and FM-B, and their application dosages on wheel-rail dynamic interactions with a range of angles of attack (AoAs) using an innovative well-controlled V-track test rig. The tested FMs have been used to provide intermediate friction for wear and noise reduction. The effectiveness of the FMs is assessed in terms of the wheel-rail adhesion characteristics and friction rolling induced axle box acceleration (ABA). This study provides the following new insights into the study of FM: the applications of the tested FMs can both reduce the wheel-rail adhesion level and change the negative friction characteristic to positive; stick-slip can be generated in the V-Track and eliminated by FM-A but intensified by FM-B, depending on the dosage of the FMs applied; the negative friction characteristic is not a must for stick-slip; the increase in ABA with AoA is insignificant until stick-slip occurs and the ABA can thus be influenced by the applications of FM.