Wave localized finite-difference-time-domain modelling of scattering of elastic waves within a polycrystalline material.
13 Dec 2018-Journal of the Acoustical Society of America (Acoustical Society of America)-Vol. 144, Iss: 6, pp 3313-3326
TL;DR: An optimal ratio of FDTD grids per grain to minimize the staircasing effects at the polycrystalline boundaries and was found to be valid over a range of grain sizes and suggests optimal averaging trials for various grain size models.
Abstract: Ultrasonic studies based on the first arrived signals are of utmost importance when dealing with heterogeneous material especially to seismology, biomedical imaging, as well as for nondestructive evaluation and structural health monitoring applications. Numerical modelling of elastic waves through polycrystalline features has been primarily held back by huge computational requirements. This article discusses the development of a robust and efficient numerical scheme based on finite-difference-time-domain (FDTD) by introducing wave-localized approach to simulate elastic waves in polycrystalline media. The numerical scheme adopts a rotated staggered grid in velocity-stress configuration. The numerical efficiency is improved by adopting parallel computing using efficient graphical processors and by introducing wave-localized computations. It is demonstrated that the proposed tool, especially with the introduction of wave-localized approach, is computationally faster and can handle large-scale grains in comparison with the commercial finite element software, especially when dealing with first arrived signals. This article reports an optimal ratio of FDTD grids per grain to minimize the staircasing effects at the polycrystalline boundaries and was found to be valid over a range of grain sizes. The article also addresses the orientation averaging requirements achieving statistically significant first arrived signal and suggests optimal averaging trials for various grain size models. The developed two-dimensional model shows good agreement with the prediction across the Rayleigh and Stochastic scattering regimes for the chosen model material (Inconel 600) having a cubic symmetry.
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TL;DR: In this paper, the development at Centre for Non-destructive Evaluation, Indian Institute of Technology Madras, of three different numerical methods, namely finite element, ray tracing and finite-difference time-domain methods for investigating the propagation of ultrasonic waves through polycrystalline media.
Abstract: The present article addresses the development at Centre for Non-destructive Evaluation, Indian Institute of Technology Madras, of three different numerical methods, namely finite element, ray tracing and finite-difference time-domain methods for investigating the propagation of ultrasonic waves through polycrystalline media. These methods are believed to aid in better understanding of ultrasonic wave interaction in materials exhibiting both simple and complex grain morphologies. The understanding is expected to provide an improved non-destructive assessment of material and defect characterisation.
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TL;DR: In this article , a numerical and experimental study on in-plane guided wave propagation in polycrystalline microstructure is presented, where Voronoi tessellation is used to generate the micro-structure considering the concept of regularity parameter.
Abstract: In this paper, a numerical and experimental study on in-plane guided wave propagation in polycrystalline microstructure is presented. For numerical study, Voronoi tessellation is used to generate the microstructure considering the concept of regularity parameter. It helped in producing equiaxed grains of microstructure, which resembles the texture of natural polycrystalline structure. In-plane guided wave propagation, resulting in simultaneous P and S wave transmission in two-dimensional (2-D) microstructure is simulated using a commercial finite element (FE) package, using graphics processing unit (GPU) based computing. Experimental verification of the in-plane guided wave propagation model is performed in the Rayleigh regime. The in-house experiments are performed on Inconel-600 plate using piezoelectric wafers as transducers. Though considerable work has been reported on P-wave characterization in a polycrystalline material, the study of in-plane guided waves is limited. It is found that within Rayleigh regime, the attenuation behavior of the in-plane guided wave shows a frequency dependency that is substantially less compared to the bulk wave in the 2-D polycrystalline microstructure. The model is first validated with the existing literature, particularly for the attenuation characterization in the Rayleigh regime. For in-plane guided waves, firstly, the numerical and experimental time-domain responses showing P and S waves are presented for different excitation frequencies. Within Rayleigh regime, the experimental and numerical group velocities and attenuation are in good agreement. Next, the attenuation characteristics are studied in the frequency range corresponding to the Rayleigh regime for different grain sizes. A new attenuation coefficient is proposed that relates the attenuation of bulk and in-plane guided waves. The study of in-plane guided wave in polycrystalline material will help in the ultrasonic investigation of defects and flaws in such materials.
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