Energy losses in viscoelastic golf balls

The compression behaviour of a number of commercial two-piece and three-piece golf balls has been determined at both low- (compression testing) and high- (impact testing) strain rates. The hysteresis determined for slow strain rate testing has been correlated with the energy losses in impact studies (coefficient of restitution values) for some two-piece balls. The core mechanical properties dominate the ball behaviour in these examples. When the two-piece ball cover has a significantly higher Shore D hardness (and hence modulus) than the core, then the cover provides constraint during loading and unloading. This reduces the viscous part of core deformation so that lower energy losses are experienced at high strain rates than that would be expected from low strain rate testing of core mechanical properties alone. The characterization of three-piece balls would suggest that the mantle (outer core) acts in a similar way to a significantly harder cover and that the ball performance is not determined solely by the core mechanical properties.