The key problem for the metallic structures’ health monitoring using the acoustic emission(AE) method is to establish a relationship between a suitable load and structures’ AE signals excited.But the current AE tests mostly use an offline loading on structures with the contact method.Here,an AE testing method using a contactless local electromagnetic online loading was proposed.Firstly,the mechanism of electromagnetically induced acoustic emission(EMAE) was studied at a microscopic level based on the electro induced dislocation and free electron movement theory.Secondly,the characteristic differences of EMAE signals under various electromagnetic loading conditions were studied,the emission characteristics of the collected nonstationary EMAE signals were studied with Hilbert-Huang transformation.Finally,the relationships among the energy percentage of intrinsic mode functions(IMFs),the cross-correlation coefficients of IMFs,the time-frequency figures of IMFs and crack orientation were established through changing the excitation direction of horizontal magnetic field.
Key words
electromagnetically induced acoustic emission /
horizontal magnetic field /
Hilbert-Huang transformation /
crack orientation
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