光纤激光干涉测量激光冲击强化自由表面速度

Measurement of free surface velocity in laser shock peening with photonic Doppler velocimetry

光纤激光干涉(PDV)是最近几年发展起来的一种新型测速技术,在某些领域已逐渐取代任意反射面测速(VISAR),但在低速且短瞬时快速变化的质点速度测量方法和数据处理技术还不成熟.本文针对激光冲击强化过程中靶材自由表面速度这一具有典型短瞬时、速度剧烈波动、速率变化大等特征的非平稳信号进行PDV测量,比较了短时傅里叶变换和连续小波变换的处理结果.研究表明,PDV对弹塑性金属材料的激光冲击强化自由表面速度能够进行准确测量,获得了符合理论分析的测量结果,特别是捕捉到了弹性前驱波;连续小波变换处理效果显著优于短时傅里叶变换.

As a newly developed instrument, photonic Doppler velocimetry （PDV） has become an ideal replacement in situations where VISAR diagnostics function poorly. However, there is a limitation on how well this technique works when the velocity of low magnitude is rapidly changing. In this paper, PDV is utilized to capture the free surface velocity history of laser shock peening （LSP）, which is a typical signal rises in nanosecond-level short time and fluctuates significantly, and methods of short time Fourier transform and continuous wavelet transform were compared in processing the interference signal. The results show that PDV is an effective diagnostic method to study the characteristics of shock pressure induced in LSP, and the temporal particle velocity profile including the elastic precursor wave is tracked. Compared to the short time Fourier transform, the continuous wavelet transform demonstrates a better temporal resolution and better interpretation to the real physical behavior.