A25 Effect of Racket Frame In-Plane Hoop Vibrations on the Coefficient of Restitution and Energy Losses in Tennis Rackets

Engineering technology has advanced to enable manufacturers to discover and synthesize new materials and new design with sport equipment. There are rackets of all compositions, sizes, weights, shapes and string tension. At the current stage, very specific designs are targeted to match the physical and technical levels of each user. However, ball and racket impact in tennis is an instantaneous phenomenon creating vibrations and large deformations of ball/strings in the racket. The problem is further complicated by the involvement of humans in the actual strokes. Therefore, there are many unknown factors involved in the mechanisms explaining how the specifications and physical properties of the high-tech rackets influence the racket capabilities. This study investigated the physical properties of various high-tech rackets, predicting racket performance in terms of the coefficient of restitution, the rebound power coefficient and the post-impact ball velocity. The coefficient of restitution e_r (COR) can be derived considering the energy loss E_1 due to racket vibrations and E_2 due to large deformations of a ball and strings corresponding to the coefficient e_ . It is based on the experimental identification of the racket dynamics and the approximate nonlinear impact analysis with a simple forehand swing model. Furthermore, it studied the effect of racket frame in-plane hoop vibrations on the coefficient of restitution and the energy losses in tennis rackets, which has been left unknowns for a long time.