基于阈值频率的激光超声缺陷检测

Laser ultrasonic defect detection based on threshold frequency

针对激光超声技术难以定量分析、检测金属样品缺陷的问题,根据不同缺陷深度处反射与透射表面波的频率交叉现象,提出了阈值频率,研究了表面缺陷深度与其对应波长的关系。通过小波分解和频谱分析,探讨和分析了反射波和透射波在频谱能量图中的波形分布特征。结果表明:由阈值频率计算的波长与缺陷深度之间的关系(即λ=4 h)与理论数据分析结果吻合良好;并随着缺陷深度的增加,波长也随之表现出线性增加的特性。由此可见,该分析方法达到了预期的效果,为表面缺陷深度的进一步定量表征提供了参考方向。

Aiming at the problem that laser ultrasonic technology is difficult to quantitatively analyze and detect defects in metal samples,a threshold frequency is proposed according to frequency cross phenomenon of reflected and transmitted surface waves at different defect depths,and the relationship between surface defect depth and its corresponding wavelength is studied.Through wavelet decomposition and spectrum analysis,the waveform distribution characteristics of reflected wave and transmitted wave in spectrum energy diagram are discussed and analyzed.The results show that the relationship between wavelength calculated from threshold frequency and defect depth(i.e.λ=4 h)is in good agreement with the theoretical data analysis results.With the increase of defect depth,the wavelength also shows a linear increase.It can be seen that the analysis method has achieved the expected effect and provided a reference direction for further quantitative characterization of surface defect depth.