Basic Research On The Mechanism Of Metal Magnetic Memory Testing And Finite Element Simulation

In this paper, the distribution characteristics of magnetic memory signals of different ferromagnetic materials under different loads were studied by numerical simulation and experiments based on the magneto-physics and magnetic technology. The laws of fatigue damage and residual life assessment using magnetic memory signals were explored.According to theory of the stress effects magnetic permeability, the finite element analysis of stress-magnetization effect was done on 20# steel plate specimen with a hole using ANSYS. The magnetic field distribution was analyzed, also the influence of the detection path and the stress state on magnetic memory signal. The curve of the peak values of the normal gradient with the stress was drawn. Through the analysis result, the normal component of the magnetic field appeared a zero-crossing point, the tangential component reaches a maximum, and magnetic flux lines reversed in the stress loading process. It proved the applicability of the magneto-elastic coupling model. Through the analysis, the stress concentration has a strong correlation with the normal gradient of the magnetic field, the stress distribution determines the gradient distribution of leakage magnetic field.The magnetic field distributions under different tensile loads were measured for no pre-defect specimens and plate notched specimens of 45# carbon steel respectively. Through the analysis, the magnetic memory signal was small and irregular in the elastic phase, but it increased apparently when the stress is greater than 500MPa. In the aspect of eigenvalue extraction, the traditional magnetic field gradient|K|max can test the stress concentration area validity. A new eigenvalue based on MMM (metal magnetic memory) signal energy was proposed. The experiment confirms that this eigenvalue can effectively detect and evaluate the ferromagnetic items. Through comparative analysis of the magnetic memory signals for 45# steel and 30CrMnSiNi2A steel in the process of tensile loads, the magnetic field gradient K changes differently under the action of stress. It has a direct relationship with the mechanical properties and magnetic parameters of the material.The fatigue crack growth experiment was carried out at room temperature for the standard SE(B) specimens of 40Cr steel, the distribution of the surface magnetic field of the specimen was investigated under the same load and different cycle numbers (N). By analyzing relations between the magnetic memory signals and the crack propagation life, the cumulative fatigue damage, a new damage parameter model was established by using magnetic memory signals. According to this model, the residual life of ferromagnetic components can be evaluated excellently. It is a basic research for the application of magnetic memory testing technology in aspects of early damage and residual life assessment of ferromagnetic materials.