铝板表面裂纹的激光超声检测与信号处理研究

Research on laser ultrasonic testing and signal processing of surface cracks in aluminum plate

为实现铝板表面裂纹缺陷检测,基于COMSOL建立铝板表面裂纹缺陷模型,分析了激光超声与缺陷的相互作用。针对激光超声在材料内部传播反射信号弱、信噪比较差的问题,提出了信号多次平均结合相邻三点信号差分处理方法。利用激光超声可视化检测系统对5 mm厚铝板表面3个裂缝进行检测,采用信号多次平均提高信噪比并增强最大振幅图中的损伤回波;提取目标区域内各扫描点信号峰峰值重构三维最大振幅图,通过相邻三点信号差分处理方法对水平、垂直方向上的超声信号进行处理,提供了更好的缺陷可见性。结果表明,表面波(R)与深度1 mm以内的表面缺陷存在明显的相互作用;激光超声可视化检测技术可快速检出铝板表面的裂纹且能够三维显示位置及大小,采用的多次平均及相邻三点信号差分处理方法能准确表征0.5 mm以上的缺陷,这将在工业无损检测及评估中有极其广泛的应用价值。

To achieve the detection of surface crack defects on aluminum plates,a surface crack defect model is established based on COMSOL and the interaction between laser ultrasound and defects is analyzed.To deal with the problem of weak reflection signals and poor signal-to-noise ratio in the propagation of laser ultrasound inside materials,a signal multiple averaging combined with adjacent three-point difference processing method.Three cracks on the surface of 5 mm thick aluminum plate were detected using a laser ultrasonic visualization inspection system.Using multiple signals averaging can increase the signal to noise ratio(SNR)and enhance the damage echo in the maximum amplitude map.Extracting the peak and peak values of the signals at each scanning point in the target area reconstructs the three-dimensional maximum amplitude map.The ultrasonic signals in the horizontal and vertical directions are processed using an adjacent three-point difference processing method,providing better defect visibility.The results show that there is a significant interaction between surface waves(R)and surface defects within a depth of 1 mm.The laser ultrasonic visualization inspection technology can quickly detect cracks and defects on the surface of aluminum plates,and can display the position and size of surface cracks in three dimensions.The multiple averaging and adjacent three-point difference processing method used can accurately characterize defects above 0.5 mm,which will have extremely broad application value in industrial non-destructive testing and evaluation.