Study on restitution characteristics of new/old rubber baseballs and metal baseball bat adapting to the new rubber baseball

• Published in: Nihon Kikai Gakkai ronbunshu
• Main Authors: Shinobu SAKAI, Daisuke YASUTOMI, Jin-Xing SHI, Akira URAKAMI, Masato MIZOGUCHI
• Format: Article
• Language: Japanese
• Published: The Japan Society of Mechanical Engineers 2019-08-01
• Subjects: sports engineering; rubber baseball; material testing; restitution characteristic; baseball bat; finite element analysis
• Online Access: https://www.jstage.jst.go.jp/article/transjsme/85/877/85_19-00118/_pdf/-char/en

In rubber baseball games, when the rubber ball is hit by a baseball bat, the rubber ball is deformed greatly comparing to an official baseball ball, and the batted ball speed decreases due to the energy loss during the deformation. Since the new rubber ball has been applied in games from 2018, the material properties and the restitution characteristics of the new rubber ball attract plenty of attention among scholars. In this study, the difference of the material properties and the restitution characteristics between the new and old rubber balls is investigated deeply by the static compression and collision tests. According to the static compression test, we find that the new rubber ball is harder and more difficult to generate deformation than the old one. In the collision test, the rebound ball speeds of both of the new and the old balls become faster when using a smaller diameter of steel cylinder instead of baseball bat, and the rebound ball speed of the new ball is slower than that of the old one under the same experimental conditions. Furthermore, to develop high performance baseball bats adapting to the new rubber baseball, the diameter of the baseball bat is studied by the impact simulation based on the finite element analysis. In the simulation, the batted ball speed under the analytical conditions of different offset heights and different barrel diameters of the bat are evaluated considering the initial spin. As a result, the batted ball speed generated by the bat with diameter φ55 mm is faster than generated by the bat with diameter φ70 mm when the offset height range is smaller than 14.6 mm, so that the bat diameter φ55 mm is recommended according to the present work.