衝撃力と慣性力が作用する一端回転支持はりの曲げ変形モデルによる木製硬式野球バットの打撃変形解析

抄録

A mechanics-of-materials deflection analysis of wooden baseball bats at impact is developed. Consider the bat which is simply supported a point of grip and elsewhere free to rotate, and the bat is subjected to the impact force with ball and the inertia force due to the sudden change of the angular velocity in swing. The static force balance gives the relation between the impact force and the inertia force, but the magnitude is left undetermined. By assuming that the impact duration is 1 ms, we get the solutions of the energy conservation equation as a function of hitting point. The present model provides the evidence for the COP (center of percussion) to be located very close to but not exactly in the sweet spot where the kinetic energy of bats can be most effectively transferred to the outgoing velocity of batted ball. Additionally, the deflection analysis determines the bending stress imposed at given velocities of bat and ball. It is shown that the largest bending stress is always located at the top of grip length irrespectively to hitting point. One hundred fifty broken bats in Hokkaido University play fields were collected and fracture surfaces were examined.