Influence of torsional stiffness of golf club shaft on its dynamic behavior during a swing

Abstract

The objective of this study was to construct a finite element (FE) model for a carbon fiber reinforced plastic (CFRP) club shaft with varying torsional stiffness, and to investigate effects of torsional stiffness of the shaft on the dynamic behavior of a golf club during the swing. The FE model of a CFRP shaft with orthotropic elasticity was composed of four-node shell elements. Mechanical properties of a prepreg composites were determined using the rule of mixture which was defined by volume fraction of fiber and resin. The torsional stiffness of shaft was varied with the Young's modulus in the range of a third part of shaft length from the tip end. The constructed shaft models can qualitatively express the torsional angle in a static analysis which loads a torque around the longitudinal axis of the shaft, and swing simulation analyses were conducted using club models which introduced the constructed shaft models. The effect of the torsional stiffness on the clubhead posture at impact tended to be stronger with the impact velocity of the clubhead because of the centrifugal force acting on the head. But, the simulation results of the posture did not necessarily depend on the torsional stiffness. This indicates that the posture of the clubhead at impact tends to be subject to effects of the timing of the impact which depends on the relationship between the ball position and the impact velocity in addition to mechanical properties of the shaft.