Velocity-dependent friction in a model of wheel–rail rolling contact and wear

Abstract

Models of rolling contact are used to predict the wear of the railhead due to passing wheels. It is commonly assumed in such models that material is worn away in proportion to the frictional work done in the slip zone of each contact patch. Moreover, a constant coefficient of friction is usually assumed. However, it is known that the friction coefficient between sliding surfaces decreases as the velocity of sliding increases. This paper describes a technique for including more sophisticated friction laws in a model of wheel–rail rolling contact. A non-Hertzian model is used based on a variational method. The resulting tangential stress distribution and slip velocity in rolling contact are examined and compared with results calculated using a constant coefficient of friction. For conditions of rolling contact with partial slip a stick–slip oscillation is found to occur when a velocity-dependent friction law is used. The pattern of material removed along the rail in rolling contact is also investigated. For low creep values and for existing broadband roughness, the inclusion of velocity-dependent friction does not result in significantly different predictions of wear. For higher creep values, velocity-dependent friction results in an unstable force–friction relationship which could lead to high variable wear.