A finite element-based deterministic multi-scale soft micro-elastohydrodynamic radial lip seal lubrication model has been set up comprising finite deformations of the elastomer surface asperities, inter-asperity cavitation and coupling of frictional heating, lubricant film temperature and lubricant viscosity. This lubrication approach essentially relies on the assumption that the lubrication of soft rough surfaces can be described by micro- or submicron-scale soft elastohydrodynamic (soft-EHL, i.e. isoviscous-elastic) lubrication at the asperity level. The overall friction thus entirely originates from the lubricant: in addition to the viscous friction contribution of the oil-filled surface roughness (meso-scale), viscous shear stresses resulting from the thin under-asperity soft-EHL oil films (submicron-scale) contribute significantly to the overall friction. The lubrication model is set up using the FEM-based multiphysics code ELMER utilizing a hydrodynamically representative sinusoidal roughness model based on the measured micro-geometry of the seal lip surface. The computed seal friction agrees well with experimental results. Moreover, this revisited soft micro EHL mixed lubrication approach is obviously capable of giving a physically sound explanation of both lubricant film formation as well as the frictional characteristics of lubricated soft rough surfaces.
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