Performance of top-of-rail products under contaminated conditions with pre-existing cracks: Impacts on traction and surface damage

Abstract

Top-of-rail (TOR) products are used to optimise friction and reduce wear in the wheel-rail contact. However, their performance is affected by the presence of oxide layers naturally formed on the rail surface and by other environmental contaminants such as water. In this study, two types of TOR products (one friction modifier and one TOR lubricant) were tested under dry and wet conditions on both clean and oxidised specimens. In addition, some specimens were preconditioned to form pre-existing cracks, allowing a comparison between undamaged and damaged surfaces. The investigation focused on traction (CoT), wear rate, and rolling contact fatigue (RCF). The results showed that, with respect to CoT, water influenced the TOR lubricant much more than the friction modifier, as it extended its retentivity and led to extremely low friction levels (CoT down to 0.05). Both products effectively reduced wear and prevented crack initiation. However, when pre-existing cracks were present, the combination of water and the liquid base of TOR products accelerated crack propagation and caused severe spalling. Interestingly, oxidation also contributed to crack growth, as oxide formation inside the crack induced internal pressure that promoted secondary crack propagation.