Keywords: twin-disc testing, wheel–rail contact, dry contact, water contamination, friction, wear.

Twin-disc testing is extensively employed to investigate the tribological behaviour of wheel-rail contacts under controlled laboratory conditions. Among the various operating environments explored in the literature, dry and water-contaminated contacts represent two fundamental reference cases for understanding friction and wear mechanisms in railway applications. Nevertheless, experimental results are often difficult to compare due to differences in testing methodologies, operating parameters and data reporting practices. In this work, a focused comparative analysis of twin-disc experimental data obtained under dry and water-contaminated conditions is presented. Literature data were systematically collected by restricting the analysis to steady-state tests, allowing a coherent interpretation of friction coefficients and wear rates as functions of slip ratio and average traction stress. The results indicate that water contamination generally leads to a reduction in wear rate with respect to dry contact, particularly at low slip ratios. However, this beneficial effect progressively diminishes as slip increases, highlighting the dominant role of traction-controlled contact mechanics. A simplified predictive relationship based on the traction parameter is proposed for both dry and water-contaminated conditions, providing an interpretable framework for engineering applications.

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