Experimental Investigation of Wheel–Rail Sliding Friction Coefficients under Varying Temperature and Humidity Conditions Using Innovative Testing Methods

The sliding friction coefficient between wheel and rail materials plays a vital role in understanding creep and contact behavior in railway systems. This study investigates its variation under controlled temperature (5–45°C) and relative humidity (50%–80% RH) conditions. A novel experimental method was proposed to eliminate the influence of atmospheric pressure and account for additional adhesion caused by surface moisture under wet friction. A counterweight was also added to improve measurement stability. Results show that low temperature and high humidity promote water-film lubrication, significantly reducing the friction coefficient. Conversely, at high temperatures and humidity, oxidation and debris formation increase friction. The frictional response exhibits clear temperature-dependent transitions, which were visualized using heatmaps and modeled via surface fitting with relatively high correlation. These findings offer both mechanistic insights and predictive tools for understanding and managing wheel–rail contact behavior under varying climatic conditions, supporting more reliable design and maintenance strategies in high-speed railway operations.