Research On The Strengthening Effect Of Excitation Magnetic Field On The Magnetic Memory Signal And Its Engineering Application

Metal magnetic memory technology is a new nondestructive testing method,the object of detection is ferromagnetic material.Evaluating the distribution and the level of the stress of the material by collecting weak magnetic signals generated by force-magnetic coupling.And it is easily affected by the environmental magnetic field when the signal is generated.However,the signal is susceptible to environmental magnetic fields.Because ferromagnetic materials are subjected to the same stress in different environmental magnetic fields,the magnetic signals generated are also different.Therefore,in the engineering application,a clear excitation enhancement mechanism is needed for guidance.In this paper,the mechanism of excitation magnetic field to enhance magnetic memory signal is researched,and the conclusion is combined with engineering practice,which is applied to the thermal residual stress detection of magnetic field assisted plasma spray welding,which widens the engineering application area of the technology.In order to investigate the enhancement mechanism of excitation magnetic field on magnetic memory signal,the static loading test of 45 steel specimens is carried out in this paper.It is found that the influence ΔH of excitation magnetic field on the force magnetic coupling is increased exponentially with the increase of stress.ΔH is the difference between the magnetic field strength affected by stress and magnetism interactively and by them individually,and it is calculated theoretically from the relationship of magnetic permeability,stress and environmental magnetic field,and it is increased with the increase of tensile stress.This is consistent with experimental results.Finally,orthogonal experiment is carried out to verify that the enhancement of the magnetic field on the stress-magnetization coupling is significant.This provides a theoretical basis for the application of the technology in magnetic field assisted spray welding quality inspection.Applying an excitation magnetic field during plasma spray welding not only improves the processing quality but also enhances the magnetic memory signature of thermal residual stress.It is found that the magnetic memory characteristic signal in the geomagnetic field is weak,and the signal under the excitation magnetic field changes obviously with the change of the concentration of the thermal residual stress.Article extracts two feature values,one of them is the difference ΔH(x)between the averagevalue and the peak value of the tangential component H(x),another is the differenceΔH(y)between peak value and valley value of the normal component H(y).It is found that these two values can be used to characterize the thermal residual stress level,and the excitation magnetic field has obvious effect on the enhancement of these two characteristic quantities.In addition,through the observation of the metallographic structure of the material after spraying,the closer the distance to the spray welding area is,the larger the grain size in the heat-affected zone is,the higher the magnetic permeability is,and the characteristic of magnetic signal is more obvious under the excitation of magnetic field.