Research On Eddy Current And Magnetic Memory Integrated Detection Method And Defect Evaluation Of Metal Components

Ferromagnetic materials and aluminium alloys are the most widely used materials in industrial applications.In the process of industrial service,cracks caused by stress concentration,corrosion and other factors directly affect the safety of components.Therefore,the use of non-destructive testing methods to prevent fracture in advance and its importance.Eddy current testing based on electromagnetic induction principle can effectively detect surface and near surface defects of conductive materials.metal magnetic memory testing based on magneto-mechanical effect can prevent damage in stress concentration area of ferromagnetic materials in advance.Based on the principle of eddy current testing and magnetic memory testing,a composite eddy current-magnetic memory testing probe is developed.The low cycle fatigue test of ferromagnetic materials is carried out.The relationship among eddy current testing,magnetic memory testing and crack length under different fatigue times is analyzed.A special multi-channel eddy current testing probe was developed for complex aluminum alloy components.The influence of the structure on the detection signal was analyzed.The change rule of the amplitude and phase of the detection signal with the lift-off height was discussed,and the linear curve was fitted.Firstly,based on 74HC4052 B chip,the schematic diagram of time-sharing circuit is drawn and printed circuit board is used to solve the problem of bridge residual voltage signal distortion.Time-sharing multiplexing test is carried out to achieve the consistency of each channel.MLX90393 sensor chip is selected to build a magnetic memory multi-channel detection module,which uses Lakeshore 421 Gaussian meter and detection sensor to measure the magnetic field value pair.It has good consistency;integrated eddy current detection module and magnetic memory detection module are in the same probe;auxiliary detection tooling is developed to realize ranging function and adjustable lift-off height function.Taking 30 CrMo steel as the research object,the experimental study of low cycle fatigue eddy current-magnetic memory composite testing was carried out.Firstly,several scanning paths were planned on the surface of the specimen,eddy current sensitivity and magnetic memory stress concentration calibration tests were carried out,and the test data were compared between the unloaded and unloaded specimens,and the plastic strain stage and micro-crack initiation stage were obtained.The change rule of magnetic memory testing signal and eddy current testing signal in the stage of segment and fatigue fracture is obtained.The response characteristics of testing signal in the whole fatigue stage and the percentage of different stages in the whole fatigue life are obtained.Based on the multi-channel eddy current testing technology,the R-angle and plane area defect detection experiments of complex aluminum alloy components were carried out.A special multi-channel eddy current testing probe was developed,the optimal detection frequency was determined,and the defect detection experiments were carried out.The defect signal and lifting-off signal had a large phase difference,which was easy to distinguish,and had a high signal-to-noise ratio.The influence of abnormal tissue on the detection signal is analyzed.Combined with metallographic observation and conductivity measurement,it is concluded that abnormal tissue causes abrupt change of conductivity and abnormal detection signal.Experiments on the influence of lift-off distance on the detection signal are carried out.The curve of the relationship between lift-off distance and the amplitude and phase of the detection signal is fitted.