Tuning raquets machanical properties on tennis player structure and skills

Modern composite materials of tennis racquets allow to join high mechanical strength and lightness. They also permit to significantly vary, zone by zone the weight and the stiffness of the frame. Due to the complexity of the present frames structure equipped with the strings, the design must be optimized by means of numerical models capable to deal with multilayer composite and impact dynamics. The objective of the process is basically to obtain light, precise, powerful and comfortable racquets. Nevertheless those attributes have very different meaning and importance for the different players' categories. Therefore a fine tuning of the design must also consider the physical structure, the aptitude and the skill of the players and the model must also take into account the contribution of the upper limb. The subjects characteristics are simply differentiated by the values of the segments masses and the shot types are distinct only by the ball-racquet impact initial conditions. As an example of this approach, local changes in frame stiffness have been correlated to the loads transmitted to the arm joints. Similar analyses demonstrated that racquet performances cannot be optimized only on the basis of central impact tests -e.g. if the frame local stiffness is very low at the middle of the racquet oval, it seems to guide the ball, after a central impact, to a un-deflected trajectory, but, when the ball hits the racquet in a point slightly displaced toward the racquet head top and top is not equipped by a large mass, it is sent out with a very angulated trajectory; on the other hand the mass on top reduce the racquet maneuverability. The predominant role of the mass distribution has also been analogously analyzed, not only with regards of the impulse transmitted to the arm but also considering the induced vibrations. The model used have been validated by means of mechanical tests on physical prototypes produced on purpose.