The Research On Welding Residual Stress Evaluated With Metal Magnetic Memory Technology

Stress is an important factor influencing and even determining the safety and reliability of the service of an engineering structure.Metal magnetic memory technology is one of the non-destructive technologies that realizes stress evaluation based on the theory of piezomagnetic pressure.It has the advantages of rapidness,safety,and high efficiency.Therefore,it has received extensive attention in the industrial field.As the service environment of engineering structures becomes more and more severe,the requirements for stress evaluation have also gradually increased,which also puts forward new requirements for metal magnetic memory evaluation stress techniques.In this paper,because metal magnetic memory technology has difficulty in quantitatively evaluating the stress damage,the metal magnetic memory normal component signal is used to test signals of defect-free sample and prefabricated crack sample and to test the change rules of signals in weld zone during static loading tensile process.The noise reduction processing technology of small packet wave is combined with normal component signal to explore the method to characterize the internal stress and damage degree of surface defect of ferromagnetic materials with metal magnetic memory technology,and to search the method to quantify internal stress of welds with metal magnetic memory technology.The main results obtained in this study are:Based on magnetic sensors,the change rules of self-emission H_p(y)magnetic-flux leakage on the surface of ferromagnetic components of different materials under different loads were studied,and relationship between magnetic memory characteristic parameters and axial stress and material types is explored.The results show that the axial stress could induce spontaneous magnetization of the ferromagnetic component,and the spontaneous magnetization increases with the increase of axial stress.The characteristic parameter K of the normal component signal has a liner relationship with the stress magnitude during the elastic deformation stage.The elastic-plastic deformation stage of the material can be distinguished according to eigenvalue K vs.stress curve.The size of characteristic parameters of different materials is different,but the characteristic parameters of the materials with higher alloying are larger.The metal magnetic memory signals can be used to characterize the surface cracks of ferromagnetic materials.When the mutation peak characteristic signal appears near the prefabricated crack defects,the characteristic parameters of signal characterizing crack size can be established by the two-dimensional weak magnetic signals of the prefabricated crack specimens with different width and depth in the static loading tensile test at different stress levels,and the Foster model is used to establish the computational formula of the limited depth and narrow slit leakage magnetic field in the magnetic memory metal detection.Based on metal magnetic memory technology,the change rules of magnetic memory curves in different welding plates and weld zones and different directions are researched,and the signals of welds in different zones are analyzed.The stress distribution situations in different zones can be calculated according to the linear relationship between characteristic parameter K of signals and the stress magnitude.The results show that the stress perpendicular to the weld is greater than the stress along the weld,and the yield limit of the material can even be reached in the heat affected zone.What's more,the magnetic memory signal perpendicular to the weld direction can better characterize the defects in weld zone,and has better application prospects.