Study On Laser-induced Ultrasonic Scanning Testing Method For Tiny Defect On Metal

Tiny flaw detection on materials helps to prevent material failure and ensure product quality and safety. Laser ultrasonic technique is a new NDT technology combined with high accuracy of laser and penetration of ultrasound, the difficulty of the study of laser ultrasonic is to design efficient laser ultrasonic testing system and to find out data processing method for broadband laser ultrasonic signals.According to the characteristics and advantages of laser ultrasonic, tiny defect detection system based on time-frequency analysis of lamb wave was designed, on the basis of this, the scanning laser ultrasonic detection system was built. Through deep study of laser ultrasonic theory and rational analysis of the experimental data, wave propagation imaging algorithm and the wave field total cumulative energy imaging algorithm were presented. Three key problems of laser ultrasonic were studied in this paper:The laser ultrasonic tiny defect detection method based on Lamb waves was proposed based on the combination of Lamb wave theory and laser ultrasonic technique. Time-frequency analysis of laser-induced ultrasonic signal was conducted through Gabor transform, tiny defect on the metal plate was recognized effectively by using this method, the detection results was intuitive and simple.Defect regions of metal plate was detected by using scanning tiny defect detection system with laser excitation and ultrasonic reception mode and measured data was processed by wave propagation imaging algorithm, the processing results was presented as movie, we could watch the propagation process of laser-induced ultrasonic wave in the metal plate directly and determine the position and size of the defect effectively, requirements of testing personnel were not high.The use of ultrasonic excitation and laser reception mode of automatic scanning detection system was effective and wave field accumulative total energy imaging algorithm was proposed, we could detect small defects and realize the defect location by this method. This algorithm was simple and fast.