AN ANALYSIS OF THE NORMAL BOUNCING OF A SOLID ELASTIC BALL ON AN OILYPLATE

An analysis is presented of the impact of a solid, elastic ball on an elastic, semi-infinite solid covered by a thin layer of lubricant. The ball is decelerated by very high hydrodynamic pressures of GPa propor tions, which also create substantial elastic deformations of the solid s as the film thicknesses fall to micrometre or sub-micrometre proport ions. The time of the impact is only slightly longer than that predict ed by classical Hertzian contact analysis. The central dimple formed i n the equivalent elastic ball near a rigid plane maintains a near cons tant film thickness as the impact proceeds, although the radius of the conjunction grows and then decays rapidly in this dynamic process. Th e minimum film thickness occurs in a ring whose rapidly changing radiu s is closely predicted by Hertzian dry impact analysis. The viscous da mping plays a modest role in the case considered, while the ball rebou nds to 95.7% of its original drop height. The pressure-time traces in the centre, and indeed at most locations in the impact zone, exhibit a remarkable second pressure peak, or spike, to yield a profile very si milar to the familiar pressure-distance trace from steady state, entra ining elastohydrodynamic lubrication problems. The findings thus confi rm the experimental observations of such pressure spikes reported in 1 985 by Safa and Gohar (Proc. 12th Leeds-Lyon Symp. Tribol, 1985). The new solution procedure outlined in the paper is expected to be useful in analysing bouncing ball arrangements, used primarily in Sweden, for theological studies of oils.