Modeling and simulation of ultrasonic beam skewing in polycrystalline materials

Abstract

Ultrasonic wave propagation through polycrystalline media results in scattering caused by the anisotropy of single grains and randomness in the orientation of the individual grains making up the polycrystal. Scattering leads to variation in phase velocity and beam skewing of elastic waves leading to a loss in energy of the forward propagating wave, significantly affecting the ability to perform material characterization, defect detection and sizing in structural components. The present work addresses the problem of beam skewing of ultrasonic longitudinal waves using FEM-based wave propagation studies in a simulated polycrystal. A well-established Voronoi tessellation algorithm is used to represent an equiaxed polycrystalline morphology. Numerical simulations are performed on beam skewing in both weak (Aluminum) and strong (Copper) anisotropic media as a function of beam launch angles. The effect of a small number of large grains and a large number of small grains on the beam quality is described. The effective refraction in polycrystals is quantified with respect to the corresponding reference isotropic media and the implications for various applications are discussed.