| Loading high frequency eddy current, the metal plate generates the stress wave under the lorentz force in the static magnetic field. The eddy currents concentrates on the interface, when there is discontinuous interface in the metal plate. The effect of lorentz force will be significantly enhanced and influences on the propagation of ultrasonic in metal plate.This paper in detail researched the multi field coupling theory of electromagnetic field, force field and displacement field in metal plate, which is loading high frequency eddy current. This paper gived the coupling equation based on the lorentz force mechanism under loading high frequency eddy current. On this basis, this paper studied the fluctuation mechanism of micro cracks interface in metal, established the three-dimensional finite element analysis model of metal plate under multi physical field,solved eddy current, magnetic field and the lorentz force in aluminum plate including the micro crack, and simulated ultrasonic wave propagation on the effect of the micro cracks in the aluminum plate.Based on the principle of nonlinear spring, this paper established the mathematical model and the finite element analysis model of closed-crack respectively and simulated the effection on ultrasonic propagation characteristics when the closed crack fluctuated in the metal plate. This paper established 2d finite element simulation model of EMAT in metal structure including closed crack, simulated vibration displacement of mass point in the propagation process of EMAT surface wave and amplitude-frequency characteristic of the mass point, analyzed the second harmonic component and studied the nonlinear propagation characteristics of EMAT surface wave in aluminum plate including closed crack. |
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