A viscoelastic split Hopkinson bar (SHB) technique is successfully applied to study dynamic behavior of a two-piece golf ball. Strain histories of the incident, reflected and transmitted waves on the input and output bars, resulting from SHB tests on cylindrical specimens of cover and core materials of the two-piece golf ball, are resolved into frequency components by Fourier transformation. Then, in frequency domain waveforms at measurement points are corrected to those at the interfaces between a specimen and bars. The complex compliance of each material is determined by calculating strain-stress ratio in the frequency domain, and 3-element viscoelastic models are subsequently identified based on variations of the complex compliances.
Using the determined viscoelastic models for the two-piece golf ball, the shape optimization of a club head is investigated by simulating the collision problem of the viscoelastic golf ball with the elastic golf club head. The basis vector method, which is an approximate method for the optimization problems, is employed to find the optimal thickness distribution of the club face so that release velocity of the ball is maximized under the constraint of a constant weight of the club head. An approach to create the basis vectors using eigenmodes of vibration is also presented. An optimal thickness distribution is obtained which raises release velocity of the ball about 5%, and it is found that this approach is effective to optimal design of club heads.
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