金属表面裂纹脉冲压缩增强型激光超声检测方法研究

Pulse compression enhanced laser ultrasonic detection method for metal surface cracks

为了提高激光超声技术检测能力,提出了一种基于脉冲压缩的增强型激光超声检测方法,并将其用于金属表面裂纹检测。该方法结合激光束空间分布调控技术,激发线性调频超声表面波信号,进一步利用匹配滤波算法对线性调频激光超声表面波信号进行脉冲压缩,可大幅度提高激光超声检测信号的信噪比和分辨率。建立空间调制激光超声数值计算模型,研究线性调频激光超声信号激励方法;基于数值模拟获得的线性调频激光超声检测信号,开发基于匹配滤波器的激光超声脉冲压缩信号处理方法;通过数值模拟不同表面裂纹缺陷与不同空间调制情况下的脉冲压缩信号效果,探究该方法对于激光超声检测信号信噪比的增强能力,并最终通过试验验证。结论表明,基于脉冲压缩技术的增强型激光超声检测方法,可以大幅度抑制噪声信号,提高针对金属表面裂纹的缺陷检测能力,解决激光超声无损检测信噪比低,灵敏度差的问题,也为该方法进一步研究提供理论依据和试验指导。

Here, to improve the detection capability of laser ultrasonic technology, an enhanced laser ultrasonic detection method based on pulse compression was proposed, and it was applied in metal surface crack detection. This method could combine laser beam spatial distribution control technology to excite linear frequency modulated(LFM) ultrasonic surface wave signal, and further the matched filtering algorithm was used to do pulse compression for LFM laser ultrasonic surface wave signal, and greatly improve signal-to-noise ratio(SNR) and resolution of laser ultrasonic detection signal. Firstly, the numerical calculation model of space modulated laser ultrasound was established to study the excitation method of LFM laser ultrasonic signal. Then, based on LFM laser ultrasonic testing signal obtained with numerical simulation, the method to process laser ultrasonic pulse compression signal was developed based on matched filter. Through numerically simulating the pulse compression signal effect under different surface crack defects and different spatial modulation, this method’s enhancement ability to SNR of laser ultrasonic testing signal was explored, and finally verified with tests. The results showed that the enhanced laser ultrasonic testing method based on pulse compression technology can greatly suppress noise signal, improve the flaw detection capability for metal surface cracks, solve problems of low SNR and poor sensitivity of laser ultrasonic nondestructive testing, and also provide theoretical basis and test guidance for further studying this method.