A simple model for friction evolution infretting

The coefficient of friction (COF) has a large influence on the material response due to fretting, and the value of the COF evolves during fretting. Friction is usually low for early cycles and increases to reach a stabilized value at locations where slip occurs between the contacting bodies. Of the fretting studies utilizing the finite element method to evaluate fretting damage metrics, only one has accounted for the evolution of friction. The majority of studies have used a constant COF equal to the stabilized value. This is not appropriate for low cycle cases where the COF is transient for the majority of the duration or for high cycle cases where the changes in COF affect the stabilized cyclic stress–strain response due to the history dependence of the material behavior. The evolution of the COF is caused by the modification of the interface between contacting materials as a result of wear processes. The wear process changes with cycling, and progresses from initial roughening from metal to metal contact, followed by accumulation of debris, followed by saturation of the debris quantity and morphology and a stabilized response. These processes are each associated with energy dissipation, which can therefore be related to the COF evolution. In this study, a simple expression for the evolution of the COF has been developed that is dependent on accumulated frictional energy dissipation density. This allows the COF to be modified in a finite element model as a function of history and location based on an experimentally measured relationship between energy dissipation andCOF.

► Friction increases in the early stages of fretting until reaching a stable value.
► A simple model captures this evolution in friction.
► Friction evolution is shown to depend on the accumulated dissipated energy density.
► A method for implementing this friction model in a finite element analysis is proposed.