Surface wave propagation for linear viscoelastic solids

Experiments have been carried out to observe the surface waves produced on large blocks of polyethylene and polymethylmethacrylate (p.m.m.) when specimens of these materials have been subjected to surface impacts of steel balls or when small lead azide charges have been detonated on the free surfaces. It has been shown that if Poisson's ratio, v, is taken to be a real constant the shapes of surface waves can be calculated if the shape of the initial disturbance and the visco-elastic properties of the medium are known. It has further been shown that the complex nature of v results in only second-order effects for the materials used. It has consequently been found possible to forecast the shape of surface waves produced by the impact of steel balls. The agreement with experimentally observed shapes was found to be excellent for the p.m.m. specimen. The theoretical predictions were less accurate for the polyethylene specimen, but the predictions here agreed reasonably well with the experiments. It was not found possible to predict the surface waves produced by the explosive charges chiefly because of uncertainty of the shape of the initial disturbance. The experimental results did, however, show two distinct groups of waves, one travelling with the dilatational velocity and the other with a velocity close to that of the shear velocity. At short distances of travel these two groups overlapped.