Role of interfacial spin in elastohydrodynamic traction contacts

Interfacial spin is an intrinsic kinematic feature of many rolling–sliding contacts, yet its specific role in elastohydrodynamic traction is still poorly understood. In this work, the effect of interfacial spin on traction behaviour and power losses in elastohydrodynamic contacts is investigated experimentally and analytically using a modified Mini Traction Machine (MTM) configuration. Spin is introduced in a controlled manner by means of a conical counter-surface, without altering the global kinematics of the test rig. Traction curves are measured over a wide range of slide-to-roll ratios, loads and rolling speeds. The results show that increasing spin systematically reduces the maximum attainable traction coefficient and shifts the onset of traction degradation towards lower slide-to-roll ratios, particularly in the low-SRR regime where traction efficiency is expected to be maximal. An energy-based analysis reveals that spin introduces an additional dissipation mechanism that dominates at low slide-to-roll ratios, while slip-related losses prevail at higher SRR values. Comparison with an isothermal elastohydrodynamic model demonstrates good agreement at low SRR, whereas increasing discrepancies at higher spin levels highlight the growing importance of thermal effects. The present results clarify the distinct role of interfacial spin in elastohydrodynamic traction and provide quantitative insights into its impact on traction performance and power losses.