Impact of a non-homogeneous sphere on a rigid surface

This paper examines the impact behaviour of a non-homogenous sphere (in this case a cricket ball with a rolled core construction) with a rigid surface. Experiments were carried out to measure the force-deflection behaviour of a cricket ball during a normal impact in two orientations (impacting on the seam and perpendicular to the seam). For the two orientations of impact, a disparity was found in terms of the force-deflection behaviour. Greater deformation was found for impacts landing on the seam, compared to those landing perpendicular to the seam. Comparisons with quasi-static test data suggested that only the bottom third of the ball may have been compressed during impact. The dynamic force-deflection behaviour was modelled using a mass attached to a Hertzian spring in parallel with a damper whose damping coefficient varied with the contact area. The coefficients in the model could be described using the velocity before impact alone. The model was found to be in good agreement with the experimental data. The model was then extended to predict oblique impacts by incorporating a measured coefficient of friction. This performed well in predicting the rebound velocity, angle and spin of a cricket ball after oblique impact with a cricket pitch. Inconsistencies in the results were attributed to deformation in the pitch surface.