An asperity-based fractional coverage model for transfer films on a tribological surface

Abstract

An asperity-based fractional coverage (AFC) model has been developed for studying the process of lubricant film transfer on a real surface. A solid/powder lubricant film is transferred to a test disk surface by intentionally shearing a compacted pellet against the rotating disk surface. A slider pad simultaneously riding on the disk can be lubricated or starved during a competition process where the pellet deposits film as the slider depletes it. The tribological behavior of this film transfer process is modeled at the asperity scale to get an understanding of the macro-scale transient and steady-state friction. The AFC model was developed for this study by extending the range of applicability of its predecessor, the control volume fractional coverage (CVFC) model, to a real tribosurface. Topography data for the tribosurface was obtained from an atomic force microscope (AFM) image of the tungsten carbide (WC) test disk. The model predicts the wear rate of the pellet, pellet/disk and pad/disk friction coefficients, and lubricant thickness as a function of the pellet load, slider pad load, disk speed, and material properties.