Advanced modelling of surface impacts from hollow sports balls

Whilst tennis racket technology has progressed significantly over the last hundred years, ball design has remained essentially unchanged. Concerns over falling interest in the sport from both players and spectators require manufacturers to be able to engineer new ball products for a wider range of playing styles and surfaces. Unfortunately, little scientific knowledge exists on the effects of ball construction upon playing characteristics, particularly how the ball behaves during the impact. Finite element analysis provides the perfect environment in which to construct complex models and interactions such as those present during a tennis ball impact. A representative set of pre-impact conditions corresponding to a range of tennis shots was selected. Various ball mesh geometries were created and a suitable set of material properties was used to develop models for uncovered rubber cores and pressurised and pressureless balls. Post impact characteristics of velocity, angle and spin were measured experimentally using high speed digital image capture techniques, together with measurements of impact force and local deformation using laser vibrometry. These results were used to verifY that the material properties used were appropriate for the strain rates present. The resulting models closely matched the experimental data. The data input file was constructed in such a way that model parameters can be easily altered by a user, providing a powerful design tool. Furthermore, the ball model may be modified with simple manipulation so that it may be generically applied to represent any hollow sports ball.