| Abstrakt: |
Location and identification of faults in multilayer elastic materials by ultrasound is aided by a physically based parametrization of the input, scattered, and detected fields. When the transducer input is beam shaped, the beam-to-mode conversion in the unflawed layered environment suggests a ''good'' parametrization in terms of a self-consistent hybrid beam-mode format. The scattered field produced by interaction of this beam-mode field with a fault zone should then be parametrized in a similar manner. This strategy guides the present investigation of scattering from a weak bonding flaw in a multilayer aluminum plate. The horizontal and vertical displacements excited by a high-frequency two-dimensional dilatational (P) Gaussian input beam have previously been tracked through successive cross sections in the perfectly bonded material [Lu et al., J. Acoust. Soc. Am. 87, 42-53 (1990)]. This input is now allowed to interact with a smoothly tapered weak-bond zone of moderate length. The equivalent forcing terms induced by the input beam are modeled in the Born approximation, and the scattered field is evaluated accordingly. Depending on the flaw size, its location relative to the input and output transducers, and other variables, the detected response at the plate surface may contain beamlike or modelike features. The beamlike phenomena are explored here with a view toward finding conditions through which the physical observables that should facilitate flaw location and identification are enhanced. Although, for convenience, the numerical data have been generated by normal-mode summation, the results reveal clearly that the hybrid beam-mode format, which remains to be developed, furnishes the proper parametrization for what is observed. [ABSTRACT FROM AUTHOR] |
