Committee F08 on Sports Equipment and Facilities has developed a new ASTM International standard that measures the stiffness and elasticity of baseballs and softballs relative to cylindrical collisions. The new standard, F2845, Test Method for Measuring the Dynamic Stiffness (DS) and Cylindrical Coefficient of Restitution (CCOR) of Baseballs and Softballs, is under the jurisdiction of Subcommittee F08.26 on Baseball and Softball Equipment.
Dynamic stiffness is a measure of a ball’s hardness. Hardness helps determine the distance an impacted ball travels — the harder the ball, the livelier it is and the farther it flies. The cylindrical coefficient of restitution, or bounciness, measures the rebound of the ball following its impact with a bat or another cylindrical object. Bouncier balls tend to be more elastic, which means that when a ball is deformed by a collision, it will reform and rebound, returning the kinetic energy of the impact into motion in the opposite direction.
According to Lloyd V. Smith, Ph.D., associate professor, School of Mechanical and Materials Engineering, Washington State University, the motivation behind the new standard is to simulate the deformation rate and magnitude of play conditions more closely than the current test methods. “Prior to F2845, ball stiffness was measured using a quasi-static method. The current tests work reasonably well, but the large difference in strain rate between the test and play conditions sometimes caused discrepancies,” says Smith.
F2845 also provides a more accurate measure of a ball’s coefficient of restitution. The increased accuracy and closeness to play conditions of the measurements can be attributed to improving on the current test methods by impacting a ball with a cylindrical surface, rather than a flat plate, and from an increased test speed that is more representative of play conditions.
The primary users of this standard will be test labs that certify balls and bats for regulating associations.
Technical Information: Lloyd V. Smith, Ph.D., Washington State University, Pullman, Wash.
ASTM Staff: Christine Basile