Development And Research Of System Of Magnetic Acoustic Emission Signal Detection And Analysis

In this paper,under the support of the National Natural Science Foundation of China(No.2016YFF0203000).Ferromagnetic metal materials are widely used in engineering and equipment manufacturing.During in-service process,wear,stress concentration,plastic deformation,corrosion and micro-damage will occur on the surface and the inside of the substrate because of cyclic load,temperature,humidity and other factors.It may cause a serious accident when the damage reaches a certain level.Therefore,it is necessary to carry out early damage detection during the in-service process of ferromagnetic metal materials.Magnetic Acoustic Emission(MAE)signal is very sensitive to the microstructure and stress state of the material.Based on this,the detection technology developed by MAE becomes a kind of promising technology of early damage detection for ferromagnetic metal materials.Based on the generation mechanism of MAE signal,this paper designs and develops a MAE signal detection and analysis system based on hardware and software,and verifies its feasibility.Based on the basic characteristics of ferromagnetic metal materials,this paper analyzes and summarizes the mechanism of MAE signal and its influencing factors.On this basis,the MAE signal detection and analysis system is designed,and the reliability was verified.The hardware of the system consists of excitation and signal acquisition.The excitation part excites the object to be inspected by establishing a suitable magnetization field.During the excitation process,the generated MAE signal is picked up and stored by the signal acquisition part;the software part is based on MATLAB graphics.The user interface(GUI)platform is developed and divided into two parts: signal acquisition and signal analysis.The signal acquisition part realizes MAE signal acquisition function with high speed,stability and continuous by setting the acquisition parameters and excitation parameters and starting and stopping the acquisition process.The signal analysis part includes the time-frequency analysis function of the MAE signal and the detection report generation function.Subsequently,with the MAE detection system,the influence of excitation conditions on the MAE signal was studied.The experiment uses a single variable method to study the MAE signals under different excitation excitation,excitation frequency and excitation of different excitation signal waveforms.Different from the existing research,it does not consider that the change of the excitation frequency will bring about the change of the excitation current at the same time,that is,the excitation frequency is changed and the excitation intensity is also changed.To avoid this problem,the power amplifier used in the experiment uses a constant current source mode.Research shows that different excitation conditions can directly affect the characteristics of MAE signals.Therefore,when applying MAE detection technology,the excitation factors should be considered comprehensively to achieve the best results.Finally,based on the pressure steel Q235 steel,the design of fatigue test was carried out to study the MAE signal characteristics of Q235 steel under different fatigue conditions,and the feasibility of applying MAE detection technology to material fatigue state evaluation was explored.At the same time,in order to avoid the accidental error caused by disassembly and assembly,the fatigue sample used in the experiment undergoes the MAE signal detection after the number of load cycles is determined,and the cyclic load is not continuously loaded thereafter.