Research On Metal Defect Detection System Based On Electromagnetic Acoustic Emission

Metal parts are widely used in modern industrial production,and many metal parts are used in high temperature,high pressure and high stress scenarios for a long time.These scenarios may lead to uneven and random distribution of stress loads on metal parts at microcracks,resulting in unnecessary economic losses and casualties.In NDT,acoustic emission technology can judge and locate the defects in all directions.However,the traditional acoustic emission technology requires the excitation source to be close to the specimen surface or the coupling agent to transform the electric field into sound field through the force field,and the traditional acoustic emission technology needs the action of external force to induce the crack acoustic emission.The electromagnetic acoustic emission（EMAE）technology studied in this paper couplings the energy from the circuit to the specimen by means of electromagnetic coupling,so it has the advantages of non-contact detection and controllable detection process.In this paper,the propagation characteristics of acoustic emission signal in metal plate and the mechanism of electromagnetic acoustic emission are systematically summarized and deduced,and then the framework and testing scheme of electromagnetic acoustic emission nondestructive testing system are designed.Then the optimal coil structure parameters are obtained by using finite element simulation software,and the influence of lift-off value on experimental results is studied.The electromagnetic acoustic emission nondestructive testing platform constructed in this paper consists of high frequency and high voltage pulse excitation module,signal conditioning circuit,signal acquisition plate,two-dimensional mechanical movement platform and upper computer.The high frequency and high voltage pulse excitation module is used to drive the coil to do electromagnetic excitation to the specimen,and the signal conditioning circuit amplifies and filters the signal output from the acoustic emission sensor to ensure that the signal output to the digital end has a high signal-tonoise ratio.For post-processing signal,according to the envelope on the acoustic emission signal in time domain and frequency domain on the envelope of gaussian function,thus obtained by gaussian function do wavelet processing of acoustic emission signal has significant advantages,in addition because sensor passband known before the test,so the idea of static wavelet to get ae signal processing and reconstruction,It can greatly reduce the redundancy of signal processing and improve the signal-to-noise ratio.The installation test of the designed detection system proves that the metal defects detection system based on electromagnetic acoustic emission designed in this paper can effectively identify the defects on the metal parts.