A New Film Parameter for Rough Surface EHL Contacts with Anisotropic and Isotropic Structures

Numerous tribological contacts worldwide rely on adequate lubrication quality for proper functionality. Despite this, there is no existing approach to accurately predict the state of lubrication. The default model since introduced in the 1960s-the Lambda -ratio, defined as the oil film thickness over the surface roughness height-is unpredictable and may yield erroneous results. Here, we put forward a framework for a new updated film parameter, Lambda*, which accounts for the elasto-hydrodynamic lubrication (EHL) effects induced by surface irregularities on the microscopic scale (micro-EHL). This new film parameter was validated in ball-on-disc tribological tests with engineering surfaces comprising isotropic and anisotropic structures. As expected, the new model was found to accurately predict the experimentally measured true mixed and full-film EHL regimes. The ability to accurately predict the mode of lubrication represents a major advance in designing tribological interfaces for optimal efficiency and durability.