Finite simulation of weld inspection using time-of-flight diffraction method based on laser ultrasonic

Conventional ultrasonic testing uses echo amplitude to characterize defect characteristics. Ultrasonic time-of-flight diffraction (TOFD) method detects defects by receiving the diffraction wave signal and uses the arrival time of the echo to characterize the defects. It is a highly accurate non-destructive testing method. Laser ultrasonic is a new type of non-contact ultrasonic excitation technology, which can obtain a wide frequency band signal without coupling and can simultaneously excite ultrasonic waves of various modes such as surface wave, transverse wave and longitudinal wave on the surface of the material. Among them, the surface wave and the longitudinal wave are not suitable for the TOFD detection because of their characteristics, so the transverse wave is used for defect detection in this paper. In this study, the finite element software ABAQUS was used to simulate the process of laser ultrasonic defect detection. According to the TOFD signal obtained by simulation, the size of the defect was calculated and compared with the actual size, and the detection error was obtained. At the same time, the effects of different defect length, width and depth on the echo signals are analyzed. The results show that the laser ultrasonic-TOFD method has good detection ability for defects with moderate length and small width, which indicates that it is feasible to apply TOFD method to laser ultrasonic flaw detection.