Study on pure squeeze elastohydrodynamic lubrication motion using optical interferometry and the inverse approach

This paper uses an optical elastohydrodynamic lubrication (EHL) impact tester to explore the effects of squeeze velocity, load, and lubricant viscosity on the dimple film thickness occurring when a ball impacts a flat plate covered by a thin layer of oil. Three types of motion for the ball are combined and simulated in this experiment to find important operation parameters. In the direct numerical solution, hydrodynamic lubrication is assumed at the initial impact stage and EHL is assumed at the high-pressure stage. Pressure and dimple shapes are obtained by numerical solution of the coupled transient Reynolds equation, elasticity equation, and ball motion equation. The inverse approach is proposed to estimate pressure and apparent viscosity in pure squeeze EHL motion. Results show that, with higher impact speeds and loads, more time is needed to reach stability. Also with lower viscosities, more time is needed to reach stability. Increasing the squeeze speed, load, and viscosity all make the dimple deeper. The post-impact high-pressure condition for the constant-load case is suitable for evaluating the pressure-viscosity index. The inverse approach is successfully used to estimate the pressure distribution resulting from the film thickness map obtained by interferometry. Agreement between the experimental value of the test fluid and the estimated value is quite good.