ELASTOHYDRODYNAMIC COLLISION AND REBOUND OF SPHERES - EXPERIMENTAL-VERIFICATION

Experiments were performed in order to delineate the conditions under which small metal and plastic spheres rebound, as opposed to stick, when dropped upon a smooth quartz surface overlaid with a thin layer of a viscous fluid. The parameters that were varied include the fluid layer thickness and viscosity, and the ball size, density, and elastic properties. The minimum drop height that allowed the ball to rebound out of the fluid layer was determined. The results are in very good agreement with the recent elastohydrodynamic theory of Davis et al. [J. Fluid Mech. 163, 479 (1986)]. Additional experiments were performed for which the quartz surface was made artificially rough by adhering fine glass spheres to it. For these experiments, the resistance to rebound caused by the fluid layer was significantly reduced, in close agreement with the recent theory for rough surfaces developed by Davis [Physico Chem. Hydrodyn. 9, 41 (1987)]. © 1988 American Institute of Physics.