| To evaluate the tribological performance of the machine components operating in the mixed lubrication regime, a contact model in mixed elastohydrodynamic lubrication is developed. This model deals with the EHL problem in very thin film region where the film is not thick enough to separate the asperity contact of rough surface. A deterministic approach to this problem is first presented in micro area where the roughness separates the asperity contact area with the lubricated area. The Fast Fourier Transform and Multigrid techniques are utilized to calculate the surface displacement, asperity contact pressure and oil film response. The load ratio, contact area ratio and average gap ratio are introduced to characterize the performance of the mixed lubrication with asperity contacts. Numerical results have shown a significant impact of the surface topography on pressure peaks.;A simpler and much faster macro-micro approach has also been developed. The relation between the average contact pressure and the average gap ratio for a typical rough contact patch is first determined numerically in micro scale. Using this relation, the average gap, average oil film pressure, and average contact pressure in a mixed-lubricated elastohydrodynamic contact can be solved simultaneously in macro scale by treating the contact to be smooth. The macro-micro approach is easy to use, computationally efficient and robust, and covers entire range of the load ratio, from unity (dry contact) to zero (full-film EHL).;The procedures of the macro-micro mixed lubrication model have been extended to the general engineered surfaces. The influences of the surface roughness, surface aspect ratio, surface auto-correlation length, and hardness of material, as well as the dimensionless load, speed, material parameters and the ellipticity parameter, on the load ratio and average gap ratio in mixed lubrication were investigated. Seventy-four different cases were used in fitting the load ratio and the average gap ratio formulas, which provide an empirical solution to the transition regime from the full-film EHL to the boundary lubrication (dry contact). |
