Modelling of elastohydrodynamic lubrication and fatigue of rough surfaces: The effect of lambda ratio

The article describes a numerical model for the analysis of elastohydrodynamic lubrication under conditions in which the nominal lubricant film thickness is small compared to the roughness present on the surfaces (lambda ratio less than unity). These conditions occur in most types of gear tooth contacts and in many other heavily loaded machine elements. In these situations, lubrication occurs at the roughness asperity level (micro-elastohydrodynamic lubrication), and in extreme cases ‘mixed’ lubrication behaviour occurs in which momentary solid contacts between the surfaces take place. In both micro-elastohydrodynamic lubrication and mixed lubrication regimes high, localised pressures are applied cyclically to asperity features as they move through the nominal contact leading to fatigue at the asperity level, which culminates in micropitting wear. Results of the modelling show the effect of lambda ratio in lubricated gear tooth contacts, and demonstrate the transition from full-film to micro-elastohydrodynamic lubrication and mixed lubrication, and the consequences in terms of predicted fatigue damage.