| Love wave is known as surface acoustic wave with shear polarization that propagate as multiple total reflection in a layered waveguide of a given material deposited on a substrate with different elastic properties. Love wave carries much information of physical parameters about layer and substrate. Love wave has a lot of characteristics, such as wide amplitude, slow attenuation, anti-interference, and so on. In this case, Love wave is especially suitable for testing and evaluating the quality of the layer with half-space structure. Love wave can test the large metal structures to achieve the rapid, large-scale and non-destructive test, but also to test and evaluate the structure underground, underwater, under cover or under the insulation layer. In the aerospace and weapons manufacturing industries, Cu-layer is often welded with a few micrometers or millimeters of the steel-substrate to improve the electrical conductivity, thermal conductivity, and surface hardness, while improving the erosion resistance of steel products. It's very meaningful to research Love wave propagating in metal plate with layers that this way can test the bond quality and increase detecting efficiency.Based on the model of Love wave propagating in half-space, the dispersion equation is studied by the way of numerical analysis using Gauss-Newton algorithm. Then, the dispersive curve of Love wave propagation in homogeneous layers was plotted in the presence of Matlab Software. The influencing factors of dispersive characteristics are discussed, such as the physical parameters of the tested materials (such as shear modulus, density), thickness of the layer and the working frequency of the driving source. In addition, wave structure of Love wave is also studied using the same way. The internal relations among wave structure and kd and modal are discussed. It is held that, the dispersion curve is characterized by the relationship among phase velocity, group velocity and the product of wave number and thickness. And the energy distribution during the propagation is characterized by wave structure. Deep awareness of the means of the dispersion characteristics and wave structure, it can choose the suitable model and frequency for Love wave testing to improve detection sensitivity according to the wave structure curve and stress distribution curve.The device for Love wave detection was designed according to the type of wave transform as being oblique incidence in different interface. The value of the group velocity and phase velocity in Cu cladding on steel substrate are tested by generating shear stresses. The cladding thickness is 0.2mm. The nominal frequency of the angle probe is 1 MHz and 2.5 MHz, and their working frequency is 0.977MHz and 2.343MHz. The regression analysis is taken for tested results which will be compared with the theoretical analysis. The error of the value of group velocity and phase velocity is 0.9% and 0.36% when the working frequency is 0.977MHz, while the error of the value of group velocity and phase velocity is 1.9% and 0.94% when the working frequency is 2.343MHz. It was found that the tested results and the analysis results are in good agreement. In addition, it was also found that the group velocity taken more dependence on frequency than the phase velocity. The value of the group velocity will decrease as frequency increasing, while the dispersion phenomena will get more severe, and decrease the sensitivity of Love wave testing for Cu cladding, so it should choose the low frequency in experiment.The research provides theory and references for nondestructive test and evaluation of layered material, such as explosion molding, coating, electric plating, etc.
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