Communication Dans Un Congrès Année : 2020

Investigation of coherent surface acoustic wave attenuation in polycrystalline materials

Résumé

The propagation of elastic waves in polycrystalline materials is a complex use case of the more general class of problems dealing with wave propagation in random, heterogeneous media. Elastic waves which are propagating in polycrystals are permanently scattered at the boundaries between adjacent grains due to an abrupt change of acoustic material properties caused by changing crystallite orientations. This leads to a macroscopic spatial attenuation in propagation direction, which is related to details of the microstructure (e.g. average grain size) and thus might be used for its characterization. Although the idea of using ultrasonic attenuation measurements for microstructure characterization exists for more than half a century, even today no direct extraction of the mean grain size of a polycrystal by inversion of acoustic attenuation measurements has been achieved. In experiments, usually longitudinal bulk waves are used, where the reliable determination of the acoustic attenuation is still challenging. Here, we utilize Rayleigh-type surface acoustic waves (SAWs), which are excited and detected with a non-contact frequency domain Laser-Ultrasound (LUS) system. A substantial advantage of SAWs is, that they can be traced along their propagation path at the sample surface, which is beneficial for the determination of the spatial wave attenuation. Moreover, the frequency-domain LUS-approach enables the generation of SAWs in a very broad frequency range, which allows for a spectroscopy-like determination of the attenuation that might prove useful when it comes to model inversion procedures. In addition, we perform time-domain finite element simulations of SAW propagation in artificially synthesized polycrystals to complement the experimental results. A Laguerre-tessellation, statistically matched to the real sample by comparison of the 2-dimensional spatial autocorrelation function, is used as a model for the granular microstructure. Frequency dependent attenuation values obtained from experiments and simulations are further compared to an analytical attenuation model and conclusions are drawn.

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Dates et versions

hal-03240228 , version 1 (13-06-2021)

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Martin Ryzy, Tomas Grabec, Istvan Veres. Investigation of coherent surface acoustic wave attenuation in polycrystalline materials. Forum Acusticum, Dec 2020, Lyon, France. pp.1833-1838, ⟨10.48465/fa.2020.0165⟩. ⟨hal-03240228⟩

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