Scattering of elastic waves from thin shapes in three dimensions using the composite boundary integral equation formulation

In this paper, the composite boundary integral equation (BIE) formulation is applied to scattering of elastic waves from thin shapes with small but finite thickness (open cracks or thin voids, thin inclusions, thin-layer interfaces, etc,), which are modeled with two surfaces. This composite BIE formulation, which is an extension of the Burton and Miller's formulation for acoustic waves, uses a linear combination of the conventional BIE and the hypersingular BIE. For thin shapes, the conventional BIE, as well as the hypersingular BIE, will degenerate (or nearly degenerate) if they are applied individually on the two surfaces, The composite BIE formulation, however, will not degenerate for such problems, as demonstrated in this paper. Nearly singular and hypersingular integrals, which arise in problems involving thin shapes modeled with two surfaces, are transformed into sums of weakly singular integrals and nonsingular Line integrals. Thus, no finer mesh is needed to compute these nearly singular integrals. Numerical examples of elastic waves scattered from penny-shaped cracks with Varying openings are presented to demonstrate the effectiveness of the composite BIE formulation. (C) 1997 Acoustical Society of America.