Study On Electromagnetic Acoustic Emission Mechanism And Experiments

Electromagnetically acoustic emission technique(EMAE) is a recently developed non-destructive test technique. Using electromagnetic stimulation to produce acoustic emission(AE) signals is used to locate small flaws or cracks in thin-walled structures nondestructively to allow inspection of specific areas without loading the whole structure. This technique allows a structure to be loaded locally by applying an Electromagnetic field in order to produce an AE response,which may be captured by conventional AE sensors. As an emerging technology, much work is needed to theoretically study its principle and application.Because there are many nonlinear problems in EMAE and the electromagnetic-structure coupling field problem is very complicated, traditional analytic method cannot get a comprehensive solution to these problems. In this paper,the finite element model of EMAE was built,and the EMAE technology is validated by a series of experiments. The research details are listed below.1.By the principle of Maxwell theory, electrically induced eddy current and Lorentz force, the principle of electromagnetic acoustic emission phenomenon has been described, and the electromagnetic field analysis method is selected.2.The EMAE incentive system is designed. Excitation signal and the drive coil of excitation system is selected and designed through the simulation analysis and theoretical calculation, and coil structure parameters and excitation signal frequency is determined.3.The simulation analysis of the EMAE is made. The EMAE aluminum model containing crack defects is established to analysis the eddy current distribution, Lorentz force distribution and strain distribution of aluminum plate with defects. All of these demonstrate the feasibility of encouraging acoustic emission with eddy current.4.The experimental platform is set up based on designed incentive system. EMAE experiments are carried out to study the influence of lift-off values and crack sizes on Lorentz force. AE signal characteristics changing with the lift-off values and depth is obtained and is the same as the simulation results. The electromagnetic acoustic emission signal distribution characteristics are obtained by using FFT and wavelet transform.