Studies On The Magnetomechanical Effect Under Weak Magnetic Field

The damage of large-scale ferromagnetic material result from stationary andcyclic loading happens frequently in the industrial area, which has drew greatattention recently. The ways to evaluate plastic deformation and fatigue in theferromagnetic material develop rapidly with the improvement of the science andtechnology. The metal magnetic memory (MMM) method is one of the mostefficient ways that was developed recently. In this article, the MMM method isused to evaluate the plastic deformation and fatigue damage in the ferromagneticmaterial.Firstly, in this thesis, the influence of plastic deformation on the magnetizationwas studied. The magnetization law results from the geomagnetic field and theplastic deformation was obtained theoretically. The magnetic domain moves tothe easy magnetization axis under the influence of outside field. In the stage ofplastic deformation, the movement of the crystal lattice leads to dislocationchange, residual stress and magnetoplastic energy, which have influence on themagnetization. Based on the J-A model, a magnetic-plastic model was obtained.In order to verify the correctness of the relationship, tensile test is conductedwith the Q235steel and45steel. The variation of magnetization with the strain inthe stage of plastic deformation is obtained with experiment. The reason ofmagnetic signal changes and the factors which have influence on the changes areanalyzed. Fatigue test is conducted with Q235steel. The computed magnetizationexhibits sharp change in the preliminary stage of plastic deformation, inagreement with experimental results. Next, this thesis also studied the anotherstate of deformation, cyclic stress-strain state. The J-A model is modified todescribe the MMM phenomena under geomagnetic field and cyclic stress. Themagnetization characteristic under cyclic stress is analyzed, and the stable stateM0that magnetization intensity M tends to is constructed. Tensile-tensile fatiguetest is conducted with the Q235steel to analyze the MMM signal variation withstress, the MMM signal variation at the process of fatigue and the MMM signaldistribution. The MMM signal changes along the circle in a stress cycle, whichverifies the rationality of M0construction. The change law of the MMM signal atthe process of fatigue and the distribution feature of the MMM signal can beexplained using the modified J-A model, which verifies the validity of themodified J-A model.