Spectral analysis of the scattering waveform of the laser-generated ultrasonic waves for detecting the crack in the material

By means of the finite element method the laser-gener ated ultrasonic wave is simulated when laser interacts on the Al surface.After the resuts are computed for the Al plates with the same thickness but different depths of surface-breaking cracks and a given depth of subsuface crak under the top surface of the Al plate,the characteristics of the reflected wave and transmitted wave generated by the Rayleigh waves interacted with the surface breaking cracds and the subsurface crack are attained.Furthermore,based on Wingner-Vile theory the spectrum of the two signals recorded on both sides of the crack are a nalyzed.The result shows that the depths of the surface cracks and the subsurface crack cause the obvious effect on the spectral characteristics.This phenomena could be useful to the laser ultrasonic quantitative non-destructive evaluation (QNDE).