Topography transformations due to running-in of rolling-sliding non-conformal contacts

A ball-on-disc machine was operated under conditions relevant to heavily loaded gears. Various levels of isotropic surface finishes were evaluated to reveal the influence on elasto-hydrodynamic lubrication (EHL). Stribeck tests were conducted for insight about roughness effects in all regimes, whereas lift-off tests were conducted to investigate the influence on running-in. A 3D surface re-location approach was developed to enable studies of the topography on exactly the same area before and after test. This helps to find asperity level details about how topographies must transform to allow a shift from the mixed- and boundary lubrication regimes, into the full film micro-EHL regime. The micro-conformity was highlighted to play a key-role for EHL lift-off that precedes the completion of running-in. [Display omitted] •Running-in and EHL lift-off was evaluated by means of isotropic surface finishes.•Friction and electrical contact resistance was simultaneously monitored.•A 3D re-location routine was proposed for evaluation of roughness at asperity scale.•Required transformations of surfaces for the onset of micro-EHL was highlighted.