Influence Mechanism of Gas Turbine Blade Thickness on Photoacoustic Signals to Guide Defect Imaging Detection

It is necessary to study the influence mechanism of blade thickness on the photoacoustic signals since material thickness will affect defect detection precision by affecting the types, velocity, and frequency of photoacoustic signals. In this article, the influence mechanism of blade thickness on sound waves is obtained by setting defects with different depths in different thicknesses areas of blades. This mechanism instructs the imaging detection and characterization of defects with different depths in different thicknesses. First, by combining with the dispersion curves, we found that there are more anti-symmetric $A_{0}$ modes in thin area. Second, different types of sound waves lead to different velocities of sound waves. The sound velocity in the thin area of the blades is 2747.58 m/s, and the sound velocity in the thick area is 2912.22 m/s. Further, compared with the thick area, the thin area has more peaks and more complex high-frequency components, but the frequency range is basically the same. Finally, the detection and characterization of blade defects are carried out by combining imaging inspection and influence mechanism. The research results can not only promote the basic research on the influence of thickness on photoacoustic signals, but also expand the application of laser ultrasound in blade defect detection.