Solitary Waves to Assess the Internal Pressure and the Rubber Degradation of Tennis Balls

Abstract

Rubber is a material present in many commodities, including tennis balls. The characteristics of tennis balls are specified by the International Tennis Federation and are evaluated using standard tests that are too cumbersome to be staged easily and quickly. In this article we present an experimental method based on the propagation of highly nonlinear solitary waves (HNSWs) to determine the internal pressure of tennis balls and to estimate rubber degradation. HNSWs are compact waves that can form and travel in a closely-packed assembly of systematically arranged particles that generally interact according to the Hertz contact law. In the study presented here, we developed a model that predicts the internal pressure of tennis balls and estimates rubber degradation by observing the waves propagating within a chain in contact with the ball to be estimated. The model was validated experimentally, by testing 18 identical balls played over a few weeks period. We found that the dynamic interaction between the waves and the rubber can successfully detect changes in internal pressure and bouncing characteristics and that these changes were barely detected using a conventional rebound test. In the future, the findings of this study may be expanded to characterize any rubber of any shape.