基于二维延时叠加的激光诱导声表面波成像研究

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.