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2003
Conference Paper
Title
Ultrasonic beam field modeling - fundamentals and applications in nondestructive evaluation
Abstract
In ultrasonic nondestructive evaluation use is made of the physical properties of elastic waves in solids in order to detect defects and material inhomogeneities. To ensure the reliability of ultrasonic inspection techniques for modern structural materials, the effects of anisotropy and inhomogeneity and the effects of non-planar component geometries on ultrasonic wave propagation have to be taken into account. In this contribution, fundamentals and applications of two analytical approaches to three-dimensional elastic wavefield calculation are presented. Based on a mathematical formulation involving Green's dyadic displacement tensor function, appropriate evaluation yields a representation of the displacement vector of transducer wavefields which is convenient for effective numerical computation. With respect to bulk wave propagation the numerical evaluation of Green's dyadic function - which is particularly tedious in the anisotropic case - is circumvented by applying a reciprocity-based approach, valid in the (point source) far-field. The presented formulation involves characteristic quantities obtained from plane wave theory and appears as a point source superposition representation including the respective point source directivities. Among a variety of methods for transducer field calculation, beam superposition has proven to be highly efficient for circular single-element apertures. A Gaussian beam approach for anisotropic media will be presented, where the Gaussian base functions have been obtained from relationships previously derived for Gaussian wave packets. Each function is furnished with coefficients fixing the beam waists and their position. The method is especially suited for beam field calculations in inhomogeneous media. Results for both isotropic materials including curved interfaces and for anisotropic media like composites and weld material are presented, covering field profiles for various types of transducers and the modeling of time-dependent rf-signals. Simulation-assisted transducer optimization is also illustrated for both single-element and multiple-element probes.
Conference
Language
English
Keyword(s)