Effect of Wheel and Rail Conditions on Contact Dynamics and Mechanics

Abstract

This study uses the Virginia Tech – Federal Railroad Administration (VT-FRA) Roller Rig to assess how different running conditions affect the wheel-rail interface (WRI) dynamics and mechanics under repeatable and precise test settings. The advanced roller rig is used to emulate wheel loads, lateral positions, angles of attack, cant angles, and creepages that commonly occur in a train. It features a quarter-scale wheel with various profiles. First, the focus was on understanding how grease and leaves reduce traction at the wheel-rail interface (WRI). The test results indicate that even small amounts of grease significantly prolong the effects of traction loss. Similarly, leaves decrease traction (also called adhesion) in a nonlinear manner. A 50% reduction in adhesion occurs at low leaf quantities under higher creepage conditions, such as on long grades or during braking. Conversely, traction-enhancing materials such as magnetite and alumina can boost traction by up to 270% when applied at the WRI in low to moderate amounts. They, however, impact wheel wear differently. The wear rate with magnetite is similar to dry rail conditions, while little wear occurs with alumina, even though it greatly increases traction. Furthermore, the study explores how curved-track geometry affects the wheel-rail contact patch through pressure-sensitive film tests and CONTACT (software) simulations. Both conformal and two-point contacts are analyzed in experiments and simulations, showing similar contact shapes. The results demonstrate that as the wheel-rail contact moves closer to the flange, pressure concentration increases while tread contact remains consistent. The contact centroid follows a Hertzian distribution for two-point contact but shifts under conformal conditions, indicating non-Hertzian behavior. The findings emphasize how curvature influences pressure distribution and highlight the need for advanced, non-Hertzian modeling to accurately represent wheel-rail contact mechanics on curved tracks. To better understand the complex dynamics of conformal and two-point contact conditions, a series of dynamic tests is performed using varying creepage and different curving parameters. The tests show an 85% reduction in tractive forces when the angle of attack (lateral creepage) is saturated, confirming its significant effect on traction loss. Under saturated lateral creepage, tangential forces reach their frictional limit, with the traction coefficient equal to the surface friction coefficient. As the contact angle increases towards the flange, the effect of Spin creepage is observed with a steady increase in tangential traction forces. CONTACT simulations closely match experimental data, validating the approach and underscoring the need to refine sign conventions in complex coordinate systems further.