Research On Nondestructive Testing Based On Metal Magnetic Memory

Under the influence of environment or the working load,ferro-magnetic material manufacturing equipment and parts will generate tress concentration or macro cracks.This condition will reduce the carrying capacity of the material and result in failure and fracture accidents.Therefore,the use of ferromagnetic materials in the process of the nondestructive testing is an important process of production safety.Metal magnetic memory testing is a newly developed nondestructive testing method,which can effectively implement the surface and near surface defects detection to achieve early diagnosis of stress concentration damage.In this paper,the principle of metal magnetic memory based on force magnetic coupling effect is studied,and simulation and experiment were carried out.Firstly,the mechanism of magnetic memory effect was explained in terms of the magnetization theory,the magnetic mechanical effect and the minimum energy principle.The characteristics of magnetic memory signal and its feature extraction in time domain were analyzed.Secondly,starting from the magnetic dipole model,the magnetic induction intensity of the magnetic field was derived,and the relationship between the leakage magnetic field and its influence factors is analyzed qualitatively.The depth effect model was established to quantitatively analyze the relationship between the depth and width of the defect,the peak value of the normal component of the leakage magnetic field and the transverse distance of the peak.Thirdly,finite element simulation is used to study the influence of defect depth,width and lift off value on magnetic flux leakage signal.Based on the study of the influence of the angle between the magnetic field and the stretching direction on the peak value of the magnetic flux leakage signal,the optimal angle between the direction of the magnetic field vector and the direction of the stretching is determined.Based on this,the finite element simulation of the effect of stress change on tensile specimen was carried out.Finally,combined with the finite element simulation,the test results of the surface defects of the multi-sample specimens and the tensile tests of the specimens under different stress were carried out.The experimental results are in good agreement with the theoretical calculation and finite element simulation results.