CONTACT AND COMPRESSION OF ELASTIC SPHERICAL-SHELLS - THE PHYSICS OF A PING-PONG BALL

We study the deformation of a thin elastic shell in different situatio ns: case (i) contact with a rigid plane; and case (ii) subject to a lo calized load. In case (i), experiments show a first-order (discontinuo us) transition between two different configurations: the first charact erized by flat contact between the shell and the rigid plane and the s econd by an inversion of curvature leading to contact with the plane a long a circular ridge. In addition, the 'slow' impact of an elastic ba ll presents, qualitatively, a highly anomalous behaviour of the restit ution coefficient due to the dissipative energy caused by the friction between the shell and the rigid plane. Case (ii) does not present a t ransition for small deformations; however, for large deformations on a spherical shell there is a symmetry breaking of the axisymmetric fold shell into corners and polygons to diminish its energy.