Finite difference predictions of P-SV wave propagation inside submerged solids. II. Effect of geometry.

To understand better direct stress wave contributions to stone fragmentation during extracorporeal shock wave lithotripsy (ESWL), the numerical formulation developed in part I is applied to study the time evolution of stress wave fields produced inside submerged isotropic elastic solids having irregular geometries. Cut spheres are used to model stones that have already had an initial fracture. Ellipses are used to approximate other deviations from a spherical geometry. The propagation and focusing of the longitudinal (P) and shear (S) wave fronts are visualized by presenting internal strain contours. Internal strain measurements are obtained from strain gauges embedded inside plaster specimens to confirm the focusing effect obtained from the concave back surfaces of the stones. Fragmentation experiments indicate damage caused by spalling and direct stress wave focusing as well as a front surface pit presumably created by cavitation activity.