Transition of the friction behaviour and contact stiffness due to repeated high-pressure contact and slip

• Published in: Tribology international Vol. 170; p. 107487
• Main Authors: Fukagai, S., Marshall, M.B., Lewis, R.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.06.2022; Elsevier BV
• Subjects: Coefficient of friction; Contact pressure; Contact stiffness; Friction; High pressure; Interfaces; Running-in; Slip; Stiffness; Torsion tests; Ultrasound reflectometry; Wheel-rail Contact; Ultrasound reflectometry; Contact stiffness; Running-in; Wheel-rail Contact
• ISSN: 0301-679X; 1879-2464
• DOI: 10.1016/j.triboint.2022.107487

A rapid increase in the friction coefficient can occur during the running-in between the wheel and rail. Although it has been found that the running-in process depends on the initial topography, the difficulty in obtaining accurate non-destructive interfacial measurements has hindered systematic investigations. In this work, four interfaces, which have different initial topographies, were continuously monitored using ultrasound reflectometry until they became conformal. A contact pressure representative of that in a wheel-rail interface was achieved by using a high-pressure torsion test approach. The transition of contact stiffness and friction coefficient with repeated slip and their relationship were investigated. Based on the experimental results, a mechanistic model for the running-in process of the contact interface was proposed. These findings will help in understanding the running-in process of the wheel-rail interface and assist in managing the wheel and rail appropriately to improve safety. A common insight into the running-in process for metal-to-metal contacts under high contact pressures has also been developed. •This study helps in understanding the running-in process of metal-to-metal contact interfaces under high contact pressures.•The differences in the running-in mechanism due to different initial roughness’ are established.•For low initial roughness, surface fracture was considered to be the dominant in increasing the friction coefficient and contact stiffness.•For high initial roughness, plastic deformation of the asperities was considered to be the dominant factor.