Numerical Simulation of Metal Defect Detection Based on Laser Ultrasound

The noncontact and wide-band characteristics of the ultrasonic signal excited by the laser make it widely used in nondestructive detection. In this paper, the finite element method is used to simulate multiple ultrasonic signal modes and the responses of them to metal defects. The simulation shows that the changes of excited Rayleigh-wave (RW) and shear-wave (SW) can be used to research the surface crack and internal defect of the sample respectively. By analyzing the reflected wave of RW and SW at the inspection point, the effects of surface crack and internal defect on the ultrasonic signals of the two modes are quantitatively compared. The results show that the time delay of the Rayleigh echo has a linear relationship to the width and transverse position of the crack, and the peak-valley difference of Rayleigh echo at the inspection point and the crack depth can also be fitted linearly. In addition, the Y component displacement of the bottom reflected SW also decays with the change of the internal defect. This simulation model provides a theoretical basis for further experimental verification basis.