Research On Laser-generated Surface Acoustic Wave Detecting Processing Surface Damages

Hard brittle material with its unique physical and mechanical properties is widely used in the aerospace, defense and other areas of the high and new technology. Its processing surface especially the subsurface damages detection is the research hotspot in the field of surface integrity. Due to the laser-generated surface acoustic wave(LSAW) can quickly and accurately test the physical and mechanical properties of the surface and subsurface of the medium, and its high sensitivity on the material surface/subsurface defects, the study has important theoretical and engineering application significance. For the application of the laser-generated surface acoustic waves in the detection of material damages, this paper studies the application of surface acoustic waves in the detection of hard and brittle materials through theoretical research, simulation calculation and experimental testing. The main contents are as follows:In the theoretical research part, the boundary conditions and the propagation equation in layered isotropic and anisotropic medium has been derived, starting from the elastic wave equation in layered piezoelectric materials. Finally the MATLAB programming and iteration method was applied to calculate the theoretical dispersion curves of surface acoustic waves, and analyzed the influence of Young's modulus on the theoretical dispersion curves.In the simulation part, according to the propagation characteristics of surface acoustic waves, geometric model of the Si crystal material was established in the ANSYS software. The surface acoustic wave propagation has been simulated in the transient dynamics module through loading the displacement function in the model. The dispersion curves have been calculated and analyzed by processing the pickup point signal. In the end, this part analyzed the impacts of damages with different Young's modulus and thicknesses on the dispersion curves.In order to further study on the application of surface acoustic wave in the hard and brittle materials detection, finally the experimental testing was done. On the basis of the theory and application of surface acoustic wave, the laser-generated surface acoustic waves experimental system has been designed and set up. And it also introduced the calculation and selection of laser type, the design of PVDF piezoelectric film sensor and digital filter. And I detected the surface acoustic wave signal effectively.Through the above research, the theoretical dispersion curves have been calculated and provide an important theoretical basis for the application of LSAW technology in the experiment. The simulation verifies the feasibility of surface acoustic wave in the damage detection of hard and brittle materials. In the end, the experimental system has been set up and successfully detected the SAW signal.