Abstract
Batters often get injured when hit by a pitch. In particular, a hit on the face or the head is extremely dangerous; therefore, the batter is obligated to wear a helmet. A baseball helmet is an important protective gear to prevent a head injury when hit by a pitch. Although the shock absorption performance of a helmet has been evaluated, the change in its impact performance when hit repeatedly has not yet been considered. This is because once a helmet receives a large impact, it is not supposed to be re-used, even if there is no visible damage to its surface. However, if the damage is not visible, there is a possibility that the damaged helmet is re-used.
In this study, a baseball ball launcher was built, and a repeat impact experiment was conducted using a ball and a head model with a helmet. The effect of the number of impacts on the acceleration of the head model was considered. When the helmet received a large impact, such that the liner material of the helmet was damaged, the acceleration of the head model was increased remarkably in subsequent impacts. Therefore, it was found that the acceleration was transmitted to the head model since the helmet was not able to absorb the impact energy of the ball after the liner material was damaged.
