ELASTOHYDRODYNAMIC LUBRICATION AT IMPACT LOADING

Experimental and theoretical studies of elastohydrodynamically lubrica ted contacts normally assume static or quasi-static conditions. Nonste ady conditions are, however, very common, e.g., in machine elements su ch as ball bearings, gears, and cam-follower mechanisms. In this paper , the case of a ball impacting a flat lubricated surface is investigat ed theoretically. This case implies transient conditions and the lubri cating effect is due to pure squeeze action in the contact. Pressure a nd film thickness distributions are computed during impact and rebound . The results of the analysis show the effects of ball mass, initial i mpact velocity, lubricant properties, and the thickness of the applied lubricant layer on, for example, minimum film thickness, maximum impa ct force, and maximum pressure. Increasing impact velocity increases t he minimum value of film thickness achieved during the total impact ti me. The damping capacity of the lubricating film is very high at low i mpact velocity and small ball mass. In fact, the damping is so high th at no rebound occurs if the velocity or the ball mass are smaller then certain critical values. The thickness of the lubricant layer has ver y little influence on the results if it is thicker than a certain valu e. If the pressure-viscosity coefficient is increased the film becomes thicker.