Effect of a compliant substrate on the rebound of a spherical shell

The impact between a spherical shell (a table-tennis ball, in practice) and a compliant silicone surface is studied. Experimentally, the potential for achieving higher reflected angular velocity on a compliant surface compared to a rigid one is explored with special attention given to the roles of friction and of the soft substrate deformability. Additionally, local observations of the contact region and potential buckling of the spherical shell are pursued. In normal incidence, the main effect of the soft substrate on the rebound is a decrease in the coefficient of restitution of the linear velocity and an increase in the duration of contact, without a clear dependence on the substrate thickness. In addition, by observing the shell geometry at contact it was found that the shell flattening prior to its buckling is smaller on a soft surface than that observed on a rigid surface. In oblique incidence, the introduction of a soft layer clearly increases the ability of the substrate to transfer spin to the spherical shell, with a significant dependence on the layer thickness. A mechanical model incorporating linear elasticity of the surface shows a good correlation with the latter experimental results.