Research On Simulation And Experiments Of Magnetic Memory Test Stress-Magnetization Effect

The thesis is aimed the magnetic memory method which is a new non-destructive inspection technology characterized by prior diagnosis based on the stress-magnetization effect. With the perspective of the magneto-physics and ferromagnetics theory, the influences of stress on magnetic flux leakage (MFL) of ferromagnetic materials were studied by simulation and experiments, the physical mechanism of the stress-magnetization effect were also discussed.Based on the theory of magneto-physics, ferromagnetics and thermodynamics, the stress-magnetization effect and the energy of ferromagnetic materials were discussed. A mode of specimen with a hole was constructed. And the simulation of stress-magnetization effect was done. Through the analysis result, in the stress concentration region, leakage of the magnetic field normal components appeared to zero, and a maximum tangential component. Magnetic flux density value is of about 0.1 few Gauss, consistent with the actual results.Tensile loading experiments of 18CrNi4A specimen were conducted in the study. The MFL distribution of specimens under tension loading condition and after removal of applied uniaxial tension at different loadings were tested by the weak magnetic measurement system. At the same time, material nonlinear simulations of stress on loaded specimens were carried out by finite element method. Then a contrast was taken between the results of magnetic measurement and stress simulation. It shows that at the stress concentration region, change of MFL were relatively weak with slight load of the specimens. With the yielding or deforming to plastic and further the changing of MFL fluctuates more distinct, and when necking emerging, a very intensive change took place. It is indicated that stress-magnetization effect is related to the microstructure of the material. When the load increased, grains would rotate to some stable tropism. With the influence of stress concentration, the spontaneous magnetization direction deviate the origin. Magnetic domain would rotate or remove, and then the magnetic charge appears in this region.At last, the tension and three point bending fatigue experiments of 18CrNi4A specimen were carried out. The regular pattern of magnetic memory signal under different stress or cycle was studied. The conclusion of MFL range and grads would improve with the increasing of the stress cycle.The conclusions by the research will contribute to really revealing the mechanism of the magnetic memory method and present basic data for early establishing the quantification and the prior evaluation standards about failure.