Research On Magnetic Signal Characteristics Of Ferromagnetic Materials In Stress Damaged Region Based On Weak Magnetic Method

Stress concentration appears in ferromagnetic materials during long-term operation.The surface of the stress concentration zone will scatter magnetic flux line,which causes magnetic signal.The weak magnetic detection,as a newly rising inspection technology,can pick up the weak magnetic signal on the surface of the stress concentration area of ferromagnetic materials,which contributes to determining the stress damage level and location of specimens.The weak magnetic detection technology is a non-destructive testing technology that possesses the advantages of being sensitive to stress,requiring no coupling agent,being quick in operation,and supporting non-contact dynamic online detection.All these benefits guarantee a good application prospect in the field of stress detection in ferromagnetic materials.However,there is a lack of systematic analysis of the weak magnetic signal characteristics of the stress damage zone,regarding ferromagnetic specimens being affected by external loads and environmental magnetic fields.Therefore,it is a must to establish a systematic magneto-mechanical relationship for the stress damage zone of ferromagnetic materials and analyze the characteristics of weak magnetic signals,which is of key significance for the application of weak magnetic detection technology in theory and engineering practice.This subject firstly studies the effect of ferromagnetic material stress on hysteresis loop through J-A theory,calculates the magnetomechanical relationship of ferromagnetic material under different external loads,and analyzes the effect of tensile stress and compressive stress on weak magnetic signal under different loads.Then,according to the spatial distribution characteristics of the weak magnetic field of ferromagnetic metal components,a magnetic charge model is established in the stress damage area,and the influence of different loads and environmental magnetic fields on the weak magnetic signal of ferromagnetic materials is systematically analyzed.Finally,the finite element method is used to solve the stress value of the stress damage area of the ferromagnetic component,and the weak magnetic signal of the stress damage area is calculated according to the magnetic charge model.The gradient eigenvalue and weak magnetic signal are established in the stress damage area.Amplitude parameters and other analysis methods are carried out.Systematic experimental results are in good agreement with the theoretical model.The research results show that when the ferromagnetic material is subjected to external loads,on one hand,the tensile stress in the elastic range will leads to the increase in weak magnetic signal.On the other hand,the compressive stress will make the weak magnetic signal of the material decrease.The magnetic charge model established in the stress damage zone reflects the spatial distribution pattern of the weak magnetic signal in the stress damage zone.The horizontal component of the weak magnetic signal has a smaller amplitude than the tangential and normal components.In experiment,the change in horizontal component of signal is not obvious with the increase of the external magnetic field,the amplitude value of the tangential component of the signal,increases approximately linearly;while the amplitude of the normal component of the signal,is relatively small.With the increase of the external magnetic field,the amplitude value of the normal component of signal,decreases linearly,which indicates that the tangential component of signal is more susceptible to the influence of the external magnetic field.Under different loads,the peak value of the gradient of weak magnetic signal in stress damage area of ferromagnetic materials changes greatly,which means the gradient peak value can effectively determine the stress level in stress damage area.Therefore,the peak value of gradient in weak magnetic signal can be used in the weak magnetic detection.This feature is fit for evaluating the degree of stress damage and provides a reference for the research on the characteristics of weak magnetic detection signals.