Tribological behavior of friction-coupling in railway turnout switch machine: effects of service conditions and surface texture

The friction-coupling in a switch machine is vulnerable to coefficient of friction (COF) drift and localized wear under complex service conditions, which may degrade its torque-limited performance. Pin-on-disk tests were conducted to clarify how normal load and rotational speed affect friction response, wear evolution, and contact stability. To further reveal the role of surface topography, a coupled contact-wear model and finite element simulations were employed to evaluate the effect of surface texture orientation. The results show that increasing normal load mainly shortens the running-in stage and reduces the initial COF, while the steady-state COF exhibits a non-monotonic dependence on load. In contrast, increasing the rotational speed markedly intensifies steady-state COF fluctuations and wear damage. Surface texture orientation has a stronger influence on wear localization than on total wear volume. The 0° and 45° orientations show similar wear volumes and shallow maximum wear depths, while the 90° orientation produces higher wear volume and more pronounced localized damage. Simulations show that the 45° texture promotes redistribution of contact pressure and migration of high-pressure regions. These findings establish a link between surface texture orientation and wear stability, providing guidance for safe operating windows and surface-topography optimization of friction-coupling.