An elastic wave propagating through a polycrystalline medium undergoes scattering, which results in attenuation of the wave’s amplitude and dispersion of its velocity. These behaviours contain information about the microstructure and could be used for material characterisation. Hence, considerable research efforts have been devoted to understanding these behaviours, including well-established theories across the different scattering regimes, e.g. [1–5].&nbsp;Recent research on 3D finite element (FE) simulations [6–11] has demonstrated good agreements with analytical solutions of the Stanke and Kino [1] and Weaver [2] type. However, while these 3D models represent actual conditions accurately and are thus generally preferred, their high computational costs – especially with polycrystalline media and very high operating frequencies – limit the computational studies to the Rayleigh and Stochastic regimes, leaving it a challenging task to reach the Geometric regime.In this study, we propose the usage of 2D FE polycrystalline models to overcome the said limitations, and to systematically study the wave scattering mechanisms and attenuation measurements at very high frequencies. First, we will introduce the nuances and challenges in configuring the 2D FE models and validate them by comparing to 3D FE results and analytical solutions. The wave behaviours within the Geometric regime are then investigated to help explain the physical significance of the Stochastic-Geometric transition, and why the attenuation profile flattens out at such high operating frequencies. The study will also highlight the relationship and dependencies of the Geometric regime with wave propagation distances.References: 
[1]. &nbsp;&nbsp; &nbsp;Stanke FE, Kino GS. A unified theory for elastic wave propagation in polycrystalline materials. J Acoust Soc Am. 1984;75(3):665–81.&nbsp; 
[2]. &nbsp;&nbsp; &nbsp;Weaver RL. Diffusivity of ultrasound in polycrystals. J Mech Phys Solids. 1990;38(1):55–86.&nbsp; 
[3]. &nbsp;&nbsp; &nbsp;Calvet M, Margerin L. Velocity and attenuation of scalar and elastic waves in random media: A spectral function approach. J Acoust Soc Am. 2012;131(3):1843–62.&nbsp; 
[4]. &nbsp;&nbsp; &nbsp;Rokhlin SI, Li J, Sha G. Far-field scattering model for wave propagation in random media. J Acoust Soc Am. 2015;137(5):2655–69.&nbsp; 
[5]. &nbsp;&nbsp; &nbsp;Turner JA. Elastic wave propagation and scattering in heterogeneous anisotropic media: Textured polycrystalline materials. J Acoust Soc Am. 1999;106(2):541–52.&nbsp; 
[6]. &nbsp;&nbsp; &nbsp;Van Pamel A, Brett CR, Huthwaite P, Lowe MJS. Finite element modelling of elastic wave scattering within a polycrystalline material in two and three dimensions. J Acoust Soc Am. 2015;138(4):2326–36.&nbsp; 
[7]. &nbsp;&nbsp; &nbsp;Van Pamel A, Sha G, Rokhlin SI, Lowe MJS. Finite-element modelling of elastic wave propagation and scattering within heterogeneous media. Proc R Soc A Math Phys Eng Sci. 2017;473(2197):20160738.&nbsp; 
[8]. &nbsp;&nbsp; &nbsp;Van Pamel A, Sha G, Lowe MJS, Rokhlin SI. Numerical and analytic modelling of elastodynamic scattering within polycrystalline materials. J Acoust Soc Am. 2018;143(4):2394–408.&nbsp; 
[9]. &nbsp;&nbsp; &nbsp;Sha G, Huang M, Lowe MJS, Rokhlin SI. Attenuation and velocity of elastic waves in polycrystals with generally anisotropic grains: analytic and numerical modelling. J Acoust Soc Am. 2020;147(4):2422–65.&nbsp; 
[10]. &nbsp;&nbsp; &nbsp;Huang M, Sha G, Huthwaite P, Rokhlin SI, Lowe MJS. Elastic wave velocity dispersion in polycrystals with elongated grains: theoretical and numerical analysis. J Acoust Soc Am. 2020;148(6):3645–3662.&nbsp; 
[11]. &nbsp;&nbsp; &nbsp;Huang M, Sha G, Huthwaite P, Rokhlin SI, Lowe MJS. Longitudinal wave attenuation in polycrystals with elongated grains: 3D numerical and analytical modeling. J Acoust Soc Am. 2021;149(4):2377–94.&nbsp;&nbsp;

2d Finite Element Modelling for Ultrasonic Attenuation Measurement in Polycrystalline Media

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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