Research On Laser-generated Surface Acoustic Wave Detecting The Mechanical Properties Of Processing Surface Damages

Laser-generated surface acoustic wave technology in detecting the mechanical properties for the affected layer of machined surface is a new research direction in the field of machined surface quality detection technology and in the field of nondestructive testing.Due to the laser-generated surface acoustic wave(LSAW)can quickly and accurately test the physical and mechanical properties for the affected layer of machined surface,the study has important theoretical and engineering application significance.The study is based on thermo-elastic mechanism of Lasergenerated surface acoustic wave and the wave propagation mechanism of Laser generated surface acoustic wave for its propagation for the affected layer of machined surface.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:Research on the mechanism of surface acoustic wave propagation for the affected layer of machined surface: The theoretical layered-medium model for the affected layer of machined surface is constructed,and the boundary conditions and propagation equations are derived by deriving theoretical formula for the propagation of surface acoustic waves in the affected layer media.The theoretical dispersion curves are calculated by programming.Research on the construction of laser saw detection platform: According to the theory of thermo-elastic mechanism of Laser-generated surface acoustic wave and the application for the principle of detecting SAW signal by using PVDF piezoelectric thin film sensor,the platform for detecting the mechanical properties for the affected layer of machined surface is built.The effective SAW signals are acquired by testing on the machined surface of the single crystal silicon sample.Research on the experimental signal processing : The frequency domain characteristics of experimental surface acoustic wave signal are obtained via the Fast Fourier Transform,the phase velocity dispersion curves of the surface acoustic waves signal is acquired by programming calculation.The young's modulus of the surface of the single crystal silicon sample is finally obtained by matching the dispersion curves of experimental signal with the theoretical dispersion curves.Through the above research,the research results of this paper could provide a theoretical layered-medium model of the affected layer on machined surface and a set of testing platform for the detection of surface damage layer of hard brittle materials.