M. Spies, ELASTIC-WAVE PROPAGATION IN GENERAL TRANSVERSELY ISOTROPIC MEDIA .1. GREENS-FUNCTIONS AND ELASTODYNAMIC HOLOGRAPHY, The Journal of the Acoustical Society of America, 96(2), 1994, pp. 1144-1157
The formalism of plane-wave spectral decomposition of elastic wave fie
lds is used to derive a simple method for solving the inverse scatteri
ng problem, which can also be regarded as a basis for further imaging
techniques. For transversely isotropic materials like fiber composites
, but also, e.g., unidirectionally grain-structured austenitic steels,
the elastodynamic dyadic and triadic Green's functions are derived in
form of their two-dimensional space-time spectral representations. Ba
sed on a theory of plane-wave propagation in these media [M. Spies, J.
Acoust. Sec, Am. 95, 1748-1760 (1994)], the resulting expressions app
ear in a coordinate-free form and contain the orientation of the mater
ials' fiber axis as an additional parameter. Thus the results are part
icularly useful for extension to the case of layered material. The for
mulation of Huygens' principle for a source-free half-space provides t
he socalled elastodynamic holography, which allows forward-backward pr
opagation of elastic wave fields in form of an integral representation
for the displacement vector. This representation is evaluated with re
spect to space and time via fast Fourier transforms, the effectiveness
of the resulting imaging algorithm is demonstrated in comparison with
the conventional isotropic algorithm used so far. The integral repres
entation mentioned above is derived for given displacement in a refere
nce plane (specimen surface), the derivation for the case of given sur
face traction will follow in the second part of this presentation, pro
viding an integral representation for the transducer field.