Basic Research About Mechanism Of Magnetic Memory Method Based On Stress-Magnetism Effect Of Ferromagnetic Materials

The thesis is aimed at the magnetic memory method that is one new non-destructive inspection method and characterized by prior inspection. Based on the magneto-physics theory, and by experiments and finite element method, the influences of stress on magnetic flux leakage (MFL) of ferromagnetic materials were studied, the mechanism of magnetic memory method were also discussed.During the experiments, a scanning device with high-order accuracy (planar 2-D positioning) was designed to help realize exactly positioning measurement of MFL of specimens. The driving circuit of scanning device was designed. Tongs were also designed to fix the probe of Gauss meter on the scanning device. For the convenience of testing, sampling software was programmed using VC++6.0 through computer. This software can control the scanning device to move in various ways, and can take real-time data from Gauss meter by RS232. Now, weak magnetic measurement system has been completed.Tensile loading experiments of 0.20%C and 0.45%C (all mass fraction) steel were conducted in the experiments. The MFL distributions of specimens under uniaxial 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, simulations of stress of 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 zone, changes of MFL were relatively weak with slight deformation of the specimens. With the deforming to plastic and further the changing of MFL exhibits more distinct, and when necking emerging a very intensive change takes place. It is indicated that magnetic memory effect is related to the microstructure of the material. The changes of MFLs were mainly induced by magneto-elastic effect with a slight deformation of material, and effected by the micro-flaws caused by disfigurements and dislocations aggregation at highly strained zones.At last, this thesis regards silicon steel and steel 20 as the research object, carries on magnetic domain observing experiments by bitter method. The result shows that changes of domains were induced by stress concentration. Maze domains were found at the stress concentration zone of above two materials.The conclusions by the research will contribute to really revealing the...