Monday, 11 October 2004 - 11:20 AM

This presentation is part of : Graduate Student Competition

Numerical Models for Ultrasonic Scattering in Polycrystals

Goutam Ghoshal and Joseph A. Turner. University of Nebraska-Lincoln, Department of Engineering Mechanics, W317.4 Nebraska Hall, Lincoln, NE 68588

The scattering of elastic waves in polycrystalline materials is relevant for ultrasonic materials characterization and nondestructive evaluation (NDE). Ultrasonic attenuation and backscatter measurements are used widely to extract the microstructural parameters such as grain size and also to detect flaws in materials. Accurate interpretation of experimental data requires robust scattering models. Such models typically assume constant density, uniform grain size and ergodicity hypotheses. The accuracy and limits of applicability of these models cannot be fully tested with experiments due to practical limits of real material processing. Here, this problem is examined in terms of numerical simulations using Voronoi polycrystals that are discretized using finite elements. Wave propagation is studied by integrating the system directly in time using a plane-strain formulation. The material properties of the individual Voronoi cells are chosen according to appropriate material distributions. Voronoi crystals with cubic symmetry and random orientations are used, making the bulk material statistically isotropic. Example numerical results for materials with various degrees of scattering that are of common interest are presented. The numerical results are presented and compared with attenuation and backscatter theories. These results are anticipated to impact ultrasonic NDE of polycrystalline media. (Work supported by US DOE)

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