Using impulse response functions to evaluate baseball bats

Abstract

In this paper, we demonstrate a new approach to evaluating the dynamic behavior of baseball bats. Using this approach we can compare the ball striking one spot on a bat versus another, and also compare the performance of one bat design versus another. We can quantity a ball striking the "sweet spot" on a bat versus the "sting" felt at the handle when the ball strikes the wrong spot. This new approach uses IRFs (Impulse Response Functions), which simulate the impact of a ball striking a bat. The IRFs are synthesized using an experimentally derived modal model of the bat. The modal data is obtained by a standard roving impact test of the bat. Two different quantitative measures are used for comparing IRFs. One measure is called the SCC (Shape Correlation Coefficient). It is a numerical measure of the co-linearity of two deflection shapes. It is the same as the FRAC (Frequency Response Assurance Criterion) calculation, but we apply it to the time domain IRFs as well as frequency domain FRFs. The second numerical measure is called the SPD (Shape Percent Difference). The SPD is a numerical measure of the difference between two deflection shapes. It not only indicates when two shapes are different, but quantifies the magnitude of their difference. The IRFs of several different baseball bats are compared using both the SCC and SPD calculations over all time samples. These measures show graphically how similar or different the impulse responses of different bats are. ©2010 Society for Experimental Mechanics Inc.