Elastohydrodynamic Lubrication at Impact Loading

Experimental and theoretical studies of elastohydrodynamically lubricated contacts normally assume static or quasi-static conditions. Nonsteady conditions are, however, very common, e.g., in machine elements such as ball bearings, gears, and cam-follower mechanisms. In this paper, the case of a ball impacting a flat lubricated surface is investigated theoretically. This case implies transient conditions and the lubricating effect is due to pure squeeze action in the contact. Pressure and film thickness distributions are computed during impact and rebound. The results of the analysis show the effects of ball mass, initial impact velocity, lubricant properties, and the thickness of the applied lubricant layer on, for example, minimum film thickness, maximum impact force, and maximum pressure. Increasing impact velocity increases the minimum value of film thickness achieved during the total impact time. The damping capacity of the lubricating film is very high at low impact velocity and small ball mass. In fact, the damping is so high that no rebound occurs if the velocity or the ball mass are smaller than certain critical values. The thickness of the lubricant layer has very little influence on the results if it is thicker than a certain value. If the pressure-viscosity coefficient is increased, the film becomes thicker.