Characterizing the Interactions between Softballs and Softball Bats for Design of Batted-Ball Performance

Abstract

Batted-ball speed (BBS) is a function of the interaction between the respective bat and ball constructions. The overall objective of the research is to study and identify bat characteristics that influence performance as quantified by BBS for a given ball construction while complying with the standards sanctioned by the respective softball associations. This objective is being achieved through a combined experimental and finite element modeling approach, and this paper will present some of those results at the current status of the overall research program. In the current work, four softballs are initially modeled in LS-DYNA as a viscoelastic material using the expression for the shear modulus G as a function of time: G(t) = G∞ + (G0+G∞)e-βt, where G∞ and G0 represent the long-term and instantaneous shear moduli respectively, β is the decay constant and t is time. The ball model is tuned using experimental COR, dynamic stiffness and quasi-static compression test data. This viscoelastic model is found to be inadequate for capturing G(t) as it varies over the speed range of interest. The Prony series G(t) = G0 [1-∑gi (1-e-t/τi)] is pursued as an alternative method to model the ball. Various DMA test methodologies are used in an effort to characterize the viscoelastic material behavior of the foam core of the softball.