Keywords: VT-FRA Roller Rig, Top-of-Rail Friction Modifier (TORFM), wheel wear, rail wear, traction, adhesion, third-body layer.

Top-of-rail friction modifiers (TORFMs) are widely used to manage wheel–rail friction, reduce wear, and maintain an acceptable traction level. However, the relationship between the applied amount of TORFM, traction recovery, and wheel surface wear remains an important practical issue. This study experimentally investigates the influence of TORFM quantity on longitudinal traction behaviour and wheel wear morphology using the VT-FRA roller rig. A biodegradable TORFM is applied to the wheel–rail contact band in light, moderate, and heavy quantities, and the results are compared with an unlubricated baseline. The tests are conducted under controlled conditions with 10.0 kN rig wheel load, 3.0 km/h running speed, 2.0% creepage, zero angle of attack, and zero cant angle. The results show that TORFM significantly delays the recovery of the traction coefficient to the unlubricated steady-state level. The recovery time increases from approximately 7 min under dry contact to 31, 39, and 52 min for the light, moderate, and heavy TORFM conditions, respectively. Normalized traction-duration analysis indicates that the light TORFM application provides the highest material efficiency. Wheel surface measurements obtained using an integrated 3D laser profiler further show that wheel wear becomes deeper and more clearly defined as the TORFM amount decreases. Although the heavy application produces the largest absolute wear reduction, the light application provides the most efficient wear protection per unit amount of TORFM.

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