Application Reseach Of Acoustic Emission Induced By Eddy Current In Metal Plate Crack Detection

In this paper, the detecting technique of acoustic emission induced by eddy current is comprehensively studied. The relationship between the finite-element analysis of cracks and electromagnetically induced acoustic emission signals is established. This study is the beneficial exploration of Ectromagnetically Induced Acoustic Emission (EMAE) for the crack qualitative and quantitative analysis, which develops the engineering-oriented applied research of EMAE. Main points of this paper as follows:(1) The current, the electromagnetic force and the deformation of EMAE are analyzed using the finite element model of EMAE which is built based on the detecting principle of EMAE. And the feasibility of acoustic emission induced by eddy current is demonstrated. In addition, the deformation nature of the defect is determined by the fracture mechanics.(2) Based on the results of the finite element analysis, performances of the power are confirmed for acoustic emission induced eddy current. Double-Transistor forward inverting circuit is chosen to build the circuit through researching the advantages and disadvantages of the various topological circuits. Double-Transistor forward inverting circuit has advantages, including simpleness, high reliability, extendibility, adjustability of output frequency. The experiment of EMAE is carried out, acoustic emission signals from defects are received and the crack is located.(3) The signal features which can be used to identify defects are revealed through comparing the spectrum of signals from different sample under different loading situations. Because the single pulse electromagnetic stimulation has the feature of the wide frequency response, the wavelet method is used to analyze the signal energy features and further analyzes the signal features of defect.(4) Electromagnetically induced acoustic emission signals and deformations of cracks of the metal plate calculated by the finite element method are normalized. According to the the acoustic emission data of Physical Acoustic Company, Kaiser Effect and the acoustic emission theory, the relationship between the acoustic emission signal and the FEA of the cracks is established, which can prove the correctness of the FEA model.