Characterization of Maple and Ash Material Properties for the Finite Element Modeling of Wood Baseball Bats

Abstract

To assist in developing a database of wood material properties for the finite element modeling of wood baseball bats, Charpy impact testing at strain rates comparable to those that a wood bat experiences during a bat/ball collision is completed to characterize the failure energy and strain-to-failure as a function of density and slope-of-grain (SoG) for northern white ash (Fraxinus americana) and sugar maple (Acer saccharum). Un-notched Charpy test specimens made from billets of ash and maple that span the range of densities and SoGs that are approved for making professional baseball bats are impacted on either the edge grain or face grain. High-speed video is used to capture each test event and image analysis techniques are used to determine the strain-to-failure for each test. Strain-to-failure as a function of density relations are derived and these relations are used to calculate inputs to the *MAT_WOOD (Material Model 143) and *MAT_EROSION material options in LS-DYNA for the subsequent finite element modeling of the ash and maple Charpy Impact tests and for a maple bat/ball impact. The Charpy test data show that the strain-to-failure increases with increasing density for maple but the strain-to-failure remains essentially constant over the range of densities considered in this study for ash. The flat response of the ash data suggests that ash-bat durability is less sensitive to wood density than maple-bat durability. The available SoG results suggest that density has a greater effect on the impact failure properties of the wood than SoG. However, once the wood begins to fracture, SoG plays a large role in the direction of crack propagation of the wood, thereby determining if the shape of the pieces breaking away from the bat are fairly blunt or spear-like. The finite element modeling results for the Charpy and bat/ball impacts show good correlation with the experimental data.

A Finite Element Investigation into the Effect of Slope of Grain on Wood Baseball Bat Durability

“…In addition, it would also be expensive with respect to the large number of bats that would need to be explored for such a study, as well as the time required to characterize the durability of all bats in the study and subsequent examination of all bat failures. An alternative and cost-effective approach is to use the finite element method to investigate how the failure mode changes as a function of SoG for a range of representative on-field relative bat/ball speeds and impact locations [6][7][8].…”

“…The Wood Handbook states that the modulus of rupture (MOR) falls very close y x z An SoG of 0°, i.e., the grain of the wood is aligned with the long axis of the bat, is alleged to be the optimal condition for bat durability. As the SoG deviates from 0°, the effective break strength, i.e., the modulus of rupture, of the wood decreases [6,[9][10][11]. Hankinson's equation can be used to quantify the effect of SoG on wood mechanical properties, PQ P sin θ Q cos θ ,…”

“…This behavior is opposite to the impact durability of northern white ash, a ring porous wood species, which demonstrates superior durability when impacted on the edge grain face [12]. Recent Charpy testing of wood corroborated these differences in the hitting surfaces for ash and maple [6]. The tighter tolerance on the allowable SoG and the change in the hitting surface for maple from the edge to face grain for the 2009 season contributed to the rate of MPFs decreasing by 30% from what was observed in 2008 [13].…”

Sports Materials Special Issue Editorial

“…Sports engineering is not always about product development and the latest innovations, with regulators often more concerned with maintaining tradition and ensuring fair and safe play. Fortin-Smith and coworkers [9,10] present two articles on finite element models for investigating wooden baseball bat durability and failure mechanisms. They are interested in preventing potentially hazardous multi-piece failures, where a fragment of a broken bat can become a dangerous high-speed projectile.…”

“…They are interested in preventing potentially hazardous multi-piece failures, where a fragment of a broken bat can become a dangerous high-speed projectile. In the first article [9] they characterised the wood used in bats, developed the models and compared them to experiments, while in the second article [10] they used the models to investigate the effect of the slope of grain of the wood on bat failure. Cole et al [11] developed finite element modelling techniques for predicting the response of artificial turf shock pads to vertical impact loading, with implications for surface design and regulation, as well as player-surface interactions.…”