Prediction of coefficient of friction for different surface topography in mixed-EHL regime

The operation of concentrated contacts observed in gearboxes, rolling element bearings, and cams/followers of valve etc of several machinery and mechanical systems in the mixed-elastohydrodynamic lubrication (mixed-EHL) regime is one of the key reasons for occurring the incident of surface contact fatigue. Due to significant asperity interactions in the mixed-EHL regime, the friction coefficient is profoundly affected by the surface topography of mating bodies. Thus, exploration of role of surface topography on coefficient of friction in mixed-EHL regime is a vital issue. This work proposed a model for investigating the effect of different surface topography on the coefficient of friction of concentrated contacts under mixed-EHL regime. The results achieved with the proposed mixed-EHL model are validated by performing rolling/sliding experiments. A good match is found between experimental and predicted coefficient of friction. Based on the investigation, it is also concluded that a surface with small fraction of summits can operate in boundary lubrication regime at high-load and low-speed conditions. A surface with lower correlation length exhibit elastic-plastic deformation at higher coefficient of friction. High value of friction coefficient is observed for rough surface (Sq > 0.5 m) at even higher rolling speed (1 m s−1).