Towards intermittent application of solid stick top-of-rail products: Influence of contact force and application time on tribological and electrical behaviour

Solid stick top-of-rail (TOR) products are widely used to reduce wheel squeal and wear at the wheel–rail interface. In current on-board systems, these products are typically applied continuously to the wheel tread using passive, spring-loaded mechanisms that have proven effective and robust in long-term railway operation. However, increasing operator demand for extended maintenance intervals places strong constraints on stick durability, particularly in high-speed operation where frictional heating and wear of the resin matrix become critical. Furthermore, standard continuous application results in unnecessary material consumption and particle generation in areas where friction modification is not required. Intermittent application, with adjustable contact force and application time, represents a promising strategy to address these limitations. Still, the influence of these parameters on solid stick behaviour has not been previously studied. The present study quantifies, using two commercial solid-stick products under laboratory conditions, how contact force and application time affect friction performance, layer retentivity, transfer behaviour, material consumption, and electrical impedance. The results show that increasing either parameter leads to a four-to fivefold increase in effective retentivity without compromising traction or braking safety. The wheel–rail impedance remained well below the threshold associated with loss of vehicle detection under all tested conditions, including higher contact forces. In contrast to liquid TOR products, the transfer of the friction layer between the contact surfaces was found to be negligible regardless of slip or contact force, with important implications for friction management system design and applicator deployment. A simplified analytical case study based on a tramline demonstrated that intermittent application can reduce material consumption by a factor of 7.7 compared to continuous application.