Influence of different excitation parameters on laser ultrasonic Rayleigh wave and surface micro-defect detection

Ultrasonic Rayleigh wave excited by laser can be used to detect surface defects. However, the change of the parameters of the excitation laser will lead to change in the time-frequency characteristics of the Rayleigh wave, which in turn affects the detection of micro surface defects. Through numerical simulation and experiments, this paper systematically studied the influence laws of excitation laser pulse energy, pulse width, spot diameter on ultrasonic Rayleigh wave amplitude in time domain and maximum effective frequency in frequency domain, established three-dimensional finite element models of laser ultrasonic detection of surface micro-defects, and revealed that with the increase of Rayleigh wave frequency, the transmitted energy decreases after the interaction of Rayleigh waves and defects. The ultrasonic detection experiment for surface micro-defects is designed. In the experiment, the excitation laser is picosecond pulsed laser, and the B-Scan images of Phi 0.1 mm and Phi 0.05 mm micro-defects under different excitation laser parameters were obtained. The laser ultrasonic fast scanning detection system based on two-dimensional galvanometer was established to detect Phi 0.05 mm defects on the surface of additive titanium alloy plate by C-Scan imaging. The micro-defects on rough surface were successfully detected under the optimal detection parameters. The research results provide a basis for the design and optimization of laser ultrasonic detection parameters of surface micro-defects.