Static and Dynamic Properties of Various Baseballs

in Journal of Applied Biomechanics
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In this study we investigated the compressive quasi-static mechanical properties and dynamic impact behavior of baseballs. Our purpose was to determine if static testing could be used to describe dynamic ball impact properties, and to compare static and dynamic properties between traditional and modified baseballs. Average stiffness and energy loss from 19 ball models were calculated from quasi-static compression data. Dynamic impact variables were determined from force–time profiles of balls impacted into a flat stationary target at velocities from 13.4 to 40.2 m/s. Peak force increased linearly with increasing ball model stiffness. Impulse of impact increased linearly with ball mass. Coefficient of restitution (COR) decreased with increasing velocity in all balls tested, although the rate of decrease varied among the different ball models. Neither quasi-static energy loss nor hysteresis was useful in predicting dynamic energy loss (COR2). The results between traditional and modified balls varied widely in both static and dynamic tests, which is related to the large differences in mass and stiffness between the two groups. These results indicate that static parameters can be useful in predicting some dynamic impact variables, potentially reducing the complexity of testing. However, some variables, such as ball COR, could not be predicted with the static tests performed in this study.

Shonn P. Hendee and Richard M. Greenwald are with the Orthopedic Biomechanics Institute, Salt Lake City, UT. Joseph J. Crisco is with the Department of Orthopaedics, Rhode Island Hospital and Division of Engineering, Brown University, Providence, RI. Direct correspondence to Richard M. Greenwald, National Institute for Sports Science and Safety, 222 Richmond St., Suite 109, Providence, RI 02903.

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