Quantitative analysis of laser-generated ultrasonic wave characteristics and their correlation with grain size in polycrystalline materials  

作　　者：徐兆文 白雪 马健 万壮壮 王超群 Zhaowen Xu;Xue Bai;Jian Ma;Zhuangzhuang Wan;Chaoqun Wang(Laser Institute,Qilu University of Technology,Jinan 250104,China)

机构地区：[1]Laser Institute,Qilu University of Technology(Shandong Academy of Sciences),Jinan 250104,China

出　　处：《Chinese Physics B》2024年第8期526-543,共18页中国物理B（英文版）

基　　金：supported in part by the Natural Science Foundation of Shandong Province,China (Grant No.ZR2023ME073);the National Natural Science Foundation of China (Grant No.51805304);the Education Department of Shandong Province,China (Grant No.2022KJ130);Qilu University of Technology (Shandong Academy of Sciences),China (Grant Nos.2023PY009,2021JC02008 and 2022GH005)。

摘　　要：Quantitative relationship between nanosecond pulsed laser parameters and the characteristics of laser-generated ultrasonic waves in polycrystalline materials was evaluated.The high energy of the pulsed laser with a large irradiation spot simultaneously generated ultrasonic longitudinal and shear waves at the epicenter under the slight ablation regime.An optimized denoising technique based on wavelet thresholding and variational mode decomposition was applied to reduce noise in shear waves with a low signal-to-noise ratio.An approach for characterizing grain size was proposed using spectral central frequency ratio(SCFR)based on time-frequency analysis.The results demonstrate that the generation regime of ultrasonic waves is not solely determined by the laser power density;even at high power densities,a high energy with a large spot can generate an ultrasonic waveform dominated by the thermoelastic effect.This is ascribed to the intensification of the thermoelastic effect with the proportional increase in laser irradiation spot area for a given laser power density.Furthermore,both longitudinal and shear wave SCFRs are linearly related to grain size in polycrystalline materials;however,the shear wave SCFR is more sensitive to finer-grained materials.This study holds great significance for evaluating metal material properties using laser ultrasound.

关 键 词：laser-ultrasonics polycrystalline materials ultrasonic time-frequency characteristics grain size 

分 类 号：TN249[电子电信—物理电子学]