Ultrasonic scattering in polycrystalline material with elongated grains

Abstract

The scattering of elastic waves in polycrystalline materials is relevant for ultrasonic materials characterization and nondestructive evaluation (NDE). Ultrasonic attenuation and diffuse backscatter measurements have been especially useful for extracting microstructural information such as grain size and for detecting flaws in materials. Accurate interpretation of experimental data requires robust scattering models. Such models often assume constant density and uniform grain size such that the scattering for grains with mainly spherical geometry is well understood. However, many structural materials are processed in such a way that the microstructure has grain elongation (e.g., from rolling). The scattering of elastic waves in such media must be understood well for design of effective materials inspection methods and for quantitative data analysis. For materials with grain elongation, the appropriate spatial correlation function is no longer isotropic such that closed-form solutions for attenuation cannot be achieved. Here, attenuation and diffuse backscatter expressions are derived as a function of wave propagation direction with respect to the axis of grain elongation. Numerical results are presented for materials of common interest under assumptions of statistical homogeneity. These results are anticipated to impact ultrasonic nondestructive evaluation of polycrystalline media. [Work supported by U.S. DOE.]