Mechanisms Of Laser Generated Surface Acoustic Wave And Its Application In The Surface Defect Inspection

Finite element method has been employed to simulate the generation of ultrasonic guided wave generated by the pulsed laser, which has been focused in the point- or ring-pattern. In addition, the finite element model of laser line source induced surface acoustic wave has been build, based on which the interaction of the laser generated SAW and surface notch on aluminates plate has been simulated in detail.The temporal and frequency domain characteristics of guided wave generated by the point laser source with varied radii and pulse durations have been investigated by the axisymmetry finite element model, the results demonstrated that the correlation between the time and frequency domain distribution of the guided wave intensity and the temporal and spatial domain characteristics of the laser energy. In addition, the interference effect of the guided wave induced by the ring-shaped laser source have been studied in detail, the results demonstrated that the focal depth of the ultrasonic modes can be controlled by the inner radius of the ring source.Based on plane strain model, line source irradiation on the aluminum plate has been polarized in two dimensional plane, and the plane strain finite element model have been established to simulate line source generated surface acoustic wave and analyze the influence on the characteristic waveform of half-width of line source.Plane strain finite element model have been used to model the interaction between laser generated surface acoustic wave and surface notch with varied depths, where the surface notch with rectangular shape is employed to represent the fatigue crack for the convenience of modeling, in addition, the reflected and transmitted coefficients for a frequency component have been calculated and employed to evaluate the depth of crack. In addition, the surface notch with a series depths and widths have been etched on the top surface to simulate the scattered process of the laser generated surface wave, the formation of two different components of the reflected Rayleigh wave have been investigate through arrival time of them.A scanning laser line source (SLLS) technique is simulated numerically by the optimized finite element model, and changes in amplitude and frequency content have been observed for ultrasound signals generated by laser scanning over a large aluminum block containing a small surface notch. The experimentally observed SLLS amplitude and...