Elastic wave scattering from bounded media with random microstructures
Zhang, Yuan
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https://hdl.handle.net/2142/20617
Description
Title
Elastic wave scattering from bounded media with random microstructures
Author(s)
Zhang, Yuan
Issue Date
1995
Doctoral Committee Chair(s)
Weaver, Richard L.
Department of Study
Mechanical Science and Engineering
Discipline
Theoretical and Applied Mechanics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Applied Mechanics
Language
eng
Abstract
A first-order Born approximation is utilized to solve the direct and inverse scattering problems of bounded infinite media with random microstructures. The inhomogeneities of the media properties due to their microstructures are assumed to be small. Relatively simple relations are obtained between the mean-square incoherently singly-scattered signal intensities and the spectral density functions of the media inhomogeneities. These simple formulas can be applied straightforwardly to the nondestructive characterization of material microstructures.
Special cases of scattering from an infinite random fluid layer, a flat solid plate and a solid half-space immersed in fluid are studied in the present work. The analyses are valid for materials with random microstructures in general, but our interest here is in polycrystalline materials and detailed analytical and numerical results are given for cubic crystal aggregates.
Although the first Born single-scattering approximation is not valid for infinite media in general, we find that it can be applied to some cases, such as those studied here, with satisfaction. It is proved that the validity of the first Born approximation is guaranteed for infinite-layer scattering problems as long as the thickness of the layer is small. As for the case of surface wave scattering from a solid half-space, the applicability of the first Born approximation is evident from the fact that leaky surface wave propagation is a very localized phenomenon.
Resonances can occur in the cases investigated here when measuring the scattered signal near some incoherent directions. Due to resonant phenomena one can achieve relatively strong incoherently scattered signals which are otherwise very weak.
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