基于二维延时叠加的激光诱导声表面波成像研究

Study on imaging of laser-induced surface acoustic wave based on 2D time-delay superimposition

激光诱导声表面波损伤成像是激光超声无损检测的难点之一,存在成像分辨率低、成像效果差、设备要求高等问题。针对这些问题,提出采用二维延时叠加成像算法提高成像质量。首先通过实验和仿真手段对激光超声扫描过程中产生的多种信号进行系统的分析,以此为基础改进激光诱导声表面波的成像算法。本文设置具有深度梯度的矩形裂纹缺陷和圆形缺陷,通过激光超声扫描平台对缺陷进行扫描检测并成像,图像清晰地反映了两种类型缺陷的形貌。成像结果表明二维延时叠加成像算法的分辨能力较能量法有显著的提高,半峰全宽不超过0.3 mm,对圆形缺陷半径与矩形裂纹长度的测量误差不超过0.4 mm,并且对缺陷深度也有一定的测量能力。

Damage imaging based on laser-induced surface acoustic wave is one of the difficult points of laser ultrasonic nondestructive testing.There exist the problems such as low imaging resolution,poor imaging effect and high equipment requirements.Aiming at these problems,propose that the 2D time-delay superposition imaging algorithm is adopted to improve the imaging quality.Firstly,through experiment and simulation,a variety of signals generated in the process of laser ultrasonic scanning are systematically analyzed.Based on this,the imaging algorithm of laser-induced surface acoustic wave is improved.In this paper,the rectangular crack defects and circular defects with depth gradient are set up.Then,the defects are scanned,detected and imaged with the laser ultrasonic scanning platform.In the images,the morphologies of the rectangular crack defects and circular defects are clearly reflected.The imaging results show that the resolution of the 2D time-delay superposition imaging algorithm is significantly improved compared with that of the energy method.The full width at half maximum is no more than 0.3 mm;and the measurement errors of the radius of the circular defects and the length of rectangular crack defects are no more than 0.4 mm.And the algorithm also has certain measurement ability for the defect depth.