Identification of Mechanical Models for Golf Ball Materials Using a Viscoelastic Split Hopkinson Pressure Bar

Abstract

A viscoelastic (polymeric) split Hopkinson pressure bar (SHPB) was used as a means of determining the dynamic characteristics of low-impedance or soft materials. The present viscoelastic SHPB consists of polymethyl methacrylate (PMMA) bars to account for the impedance mismatch between test specimens and metallic bars. Wave propagation analysis of strain pulses in a PMMA bar was executed in the frequency domain to identify its mechanical model using elementary one-dimensional wave theory. The SHPB made of PMMA bars was applied to evaluate the high strain rate compressive properties of core and cover materials for a two-piece golf ball within nearly 0.10 strain. Complex compliances of polybutadiene rubber (core) and ionomer resin (cover) specimens, which are the ratios of the strain to stress in the frequency domain, were determined to identify the respective mechanical models. To validate the accuracy of the mechanical models for golf ball materials, finite element investigations on axial collisions between the golf ball and a long elastic bar were conducted for comparison with measured contact force histories. It is demonstrated that three-element solid models can describe the dynamic behavior of both the core and cover materials within a given frequency range. The limitations of the models are also discussed.