ASA 125th Meeting Ottawa 1993 May

5pPA1. The influence of boundary layer on elastic wave scattering by spherical inclusions.

Daniel Levesque

Luc Piche

Indust. Mater. Inst., Natl. Res. Council, 75 De Mortagne Blvd., Bouchervill, PQ J4B 6Y4, Canada

The influence of a boundary layer on the scattering of elastic waves by spherical inclusions is investigated. Based on the exact transition matrix (T) developed for layered obstacles [A. Bostrom, J. Acoust. Soc. Am. 67, 399--413 (1980)], a numerical study is performed for all values of h/a, where h is the layer thickness and a is the effective radius of the layered obstacle. For h/a << 0.1, the layer behaves like an interface, allowing one to investigate a wide range of boundary conditions. Except for high mass density interfaces, the scattered field amplitude is sensitive mainly to the normal and transverse stiffnesses and classical solutions for the so-called rigid and slip boundary conditions are recovered. For h/a<0.1, the layer acts as an interface region and property changes of the host near the obstacle can be modeled. Ultrasonic measurements with charge-filled polymers present evidence for such a layer. Finally, for h/a(approximately equal to)0.1, the layer behaves as a coating or a shell depending on the mass density. In this case, full interactions are included in the formalism.