The Effect Of Knob End Loading And Barrel Length On Mechanical Characteristics Of Aluminium Softball Bats

Abstract

Studies examining the effects of interior loading on the location of the center of percussion (COP) of aluminum softball and baseball bats have resulted in recommended procedures for the systematic displacement of the COP. However, these studies did not consider the effects of loading strategies on vibrational characteristics which may be related to bat effectiveness and annoyance. The purpose of this study was to determine the effects of knob end loading and barrel length on fundamental frequency and location of the nodes and COP. Subjects were 18 softball bats (CU31 aluminum alloy) specifically constructed for this study by a bat manufacturing firm. Six bats were fitted with conventional hollow aluminum knobs (21.9+0.5 g), six were fitted with solid aluminum knobs (74.5+0.1 g), and six were fitted with solid steel knobs (190.8+0.1 g). Two bats of each type had barrel lengths of 4.92 cm, 4.41 cm, and 3.43 cm. Standardized procedures were used to measure the moment of inertia, center of percussion location, fundamental frequency (free-free), and node locations. Results indicated that: (1) knob end loading displaced the COP toward the barrel end of the bat, increased the distance between the distal node and COP, and decreased the fundamental frequency; and (2) increasing the barrel length increased the fundamental frequency. Both variables resulted in a decrease of approximatgely 50 per cent in fundamental frequency. Effects appear to be linear and additive with no interactions. This study was partially supported by the Kansas State University Research Foundation.