Research On Simulation And Experiments Of Pulsed Magnetic Flux Leakage With U-shaped Sensor

The transient magnetic flux leakage testing technology is the most important of NDT detection methods and has the developing prospects in magnetic component.It has so many advantages such as the fast response speed,high detection sensitivity,easy to test and evaluate the defect of component.It has significant research value about the inspection and assessment of the ferromagnetic material.Based on the research dynamic of the magnetic flux leakage detection technology at home and abroad,it was adopted as the research method which combined the finite element simulation and experimental validation.This paper conducted the system research in pulsed magnetic flux leakage technology about some aspects such as the sensor's structure design,parameter optimization,defect detection,stress evaluation in ferromagnetic component.The main contents of research are as follows:First,the detection mechanism of pulse magnetic flux leakage detection is analyzed.Based on the theory of electromagnetism,the refraction principle of magnetic induction line,the forming mechanism of magnetic leakage and the testing mechanism of magnetic flux leakage are analyzed.The size and distribution of the leakage magnetic field which was interacted between the defect of the test specimen and the electromagnetic field are analyzed.The eigenvalues of the defects are extracted according to the response signals and the defects are quantitatively evaluated.Second,the finite element simulation of the magnetic flux leakage detection in ferromagnetic components.Based on the analysis of PMFL detection mechanism,the U-shaped pulse magnetic flux leakage sensor is established by finite element simulation method.The simulation results of the excitation coil structure parameter,the sensor lift height and the U-shaped yoke structure size are compared and a high sensitivity of the U-shaped sensor structure is determined.The magnetic field distribution between the U-shaped probe and the specimen under different depth defects is analyzed by simulation,and the magnetic leakage is existed in the surface defect but the pulsed reluctance is mainly existed in the subsurface defect.In order to further improve the detection sensitivity of the leakage magnetic field in three directions,based on the principle of pulse magnetic flux leakage and pulsed eddy current detection,a pulsed magnetic concentration detection method is proposed.The detection accuracy of the pulsed magnetic flux leakage and the pulsed magnetic concentration is compared from the simulation result,and the feasibility of the new detection method is analyzed.The characteristics of the internal conductivity and permeability in ferromagnetic specimen are simulated and analyzed.The characteristic values of the internal conductivity and permeability are extracted.The application of stress quantitative assessment using pulsed magnetic flux leakage is provided.Finally,experimental study on pulsed magnetic flux leakage detection in ferromagnetic components.In order to prove the accuracy and reliability of the simulation results of the pulsed magnetic flux leakage detection mechanism in ferromagnetic specimen,the corresponding experimental system is designed and the appropriate response signal noise reduction filtering method is selected.The feasibility of the proposed method which was fused the pulsed magnetic flux leakage and pulsed reluctance is verified by the simulation results,which can be used to detect and evaluate the defects of the surface and subsurface of the ferromagnetic components.The feasibility of the pulsed magnetic concentration detection method is verified by comparing with the the pulse magnetic flux leakage detection method.The relationship between the differential stress of the pulsed electromagnetic response signals and the tensile stress in ferromagnetic specimen is verified by experiments.The detection mechanism of the pulsed magnetic flux leakage stress testing method is established.