Ultrasonic characterization of synthetic three-dimensional polycrystals

Abstract

Ultrasonic nondestructive testing has been increasingly used to characterize heterogeneities of polycrystalline materials. With such techniques, the interactions of coherent ultrasonic waves with grain boundaries result in scattering. Such scattered waves carry information regarding the physical properties of the scatterer. Therefore, microstructural information can be obtained by quantifying the scattered response. Current diffuse ultrasonic backscatter models include several assumptions about the macroscopic and microscopic properties of the polycrystals. In this presentation, the sensitivity of grain size characterization to such assumptions is investigated using simulated microstructures. Several polycrystals with cubic crystal symmetry and randomly oriented grains are simulated using Dream.3D. This study applies the single scattering model in which the longitudinal-to-longitudinal configuration is considered for the incident and the scattered waves and limited to the weakly-scattering regime. In each configuration, the theoretical results are compared with results from the synthetic volumes. The results demonstrate distinct differences between the theory and the simulation. For example, the theoretical scattering cross section for a Voigt-averaged copper polycrystal at 15 MHz is found to be about three times larger than the value based on the Dream.3D microstructure. Finally, the influence of grain size distribution and grain elongation on the ultrasonic models are investigated.