Experimental and Analytical Determination of Elastic Moduli in Anisotropic Physical Models: Comparison with Equivalent Media Theories
Julie A. Hood, R. B. Mignogna, N. K. Batra, K. E. Simmonds, H. H. Chaskelis, 1996. "Experimental and Analytical Determination of Elastic Moduli in Anisotropic Physical Models: Comparison with Equivalent Media Theories", Seismic Anisotropy, Erling Fjær, Rune M. Holt, Jaswant S. Rathore
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An inversion method ispresented which provides a means to solve for the elastic moduliof anisotropic materials with symmetry as complicated as triclinic. Anisotropic elastic moduli were determinedfora layered glass plate—epoxy composite from oblique angle time—of—flight measurements using an immersion system. Both the glass and the epoxy behaveas isotropic materials in bulk form. However, once assembled to produce a heterogeneous structure(composite material) and probed with sufficiently long wavelengths, the heterogeneous stack appeared homogeneous but with anisotropic properties. With the measured properties of the constitutive bulk glass and epoxy and knowledge of their ratio in the layered stack,forward calculations are made to predict equivalent elastic moduli of the composite. Of theequivalent media theories available, a thickness—weighted averaging model as well as a theory which models the thin compliant epoxy bonds as a set of fractures are considered. Anisotropic elastic moduli predicted using these two theories are then compared to the measured elastic moduli of the glass—epoxy stack. The results show that epoxy does not behavethe same in an adhesive bond as it does in bulk. We therefore can not recommend using epoxy in the construction of physical models. However, in spite of the indeterminate behavior of epoxy, the equivalent media theories of Backus and of Schoenberg worked fairly well.