Elastic wave in homogeneous and layered transversely - isotropic media. Gaussian wave packets and green functions -QNDE-.

The increasing use of composites and composite laminates requires extensive efforts in deveolping NDE methods for these sophisticated materials. The main problem, especially with respect to algorithmic imaging, arises from their anisotropic nature which causes the splitting of phase- and group velocity directions; in layered sturctures additional difficulties are associalted with multiple reflection and transmission. For unidirectional composites, exhibiting transversely-isotropic symmetry, plane wave solutions of the elastodynamic equation of motion were derived yielding slowness- and group velocity diagrams. The propagation of Gaussian wave packets in unidirectional homogenous and layered structures has been calculated for arbitrary layer orientations; the results are shown as time domain wavefront snapshots. Finally, an integral representation of the Green's function for the transversely-isotropic medium has been derived via spatial Fourier-transforms, being particularly convenient to provide the vasis for imaging in terms of Diffraction Tomography