Theoretical Evaluation of Ultrasonic Scattering by Flaws in Anisotropic Media

Ultrasonic inspection plays an important role in numerous industrial fields. One of the prominent tasks is the determination of location, shape, size and orientation of defects. In isotropic materials, the location of reflectors can be inferred from time-of-flight measurements, angle of insonification and transducer position. In anisotropic media, however, such a procedure is aggrevated by several phenomena, which are the direction dependence of the ultrasonic velocities, the beam skewing effect and the modified radiation characteristics of flaws with respect to wave scattering. In this contribution, analytical relationships are presented for the scattering of ultrasound at defects in such media. Based on the mathematical formulation of Huygens' principle, these relationships are obtained for traction-free scatterers using Krichhoff's approximation. Asymptotic evaluation yields explicit expressions, which are further incorporated in the Generalized Point Source Synthesis method. Numeri cal results are obtained for rectangular and circualr reflectors, selected to compare with notches and flat-bottomed holes, respectively. Evaluation is performed in view of the radiation characteristics of these defects, conside ring (quasi-) longitudinal wave scattering in transversely isotropic weld material. Also, the elaborated relationships have been applied to calculate echo dynamic curves in dependence of transducer position for pulse-echo technique. Good comparison with experimental results has been obtained.