The Study Of Magnetic Memory Testing Based On Pseudo-static Test For Column And Beam-column Joints

As a new non-destructive testing technology,Metal Magnetic Memory Technology has more advantages than traditional non-destructive testing technologies.It can not noly detect macroscopic defects of ferromagnet,but also can detect early invisible damages of ferromagnet.Since this technology was put forward by scholar Doubov from Russia,it has received wide attention from international scholars.This technology is based on the magneto-mechanical effect principles of the ferromagnet,it can detect magnetic field leakage intensity in the stress concentration area of ferromagnet by the detection of megnetic memory signals of surface.However,this technology is still in the stage of development,its theoretical research and experimental research are not thorough.Most experimental researches are aiming at ferromagnetic components,which are in uniaxial state,experimental researches of complex stress state components are fewer.Therefore,this paper mainly does the experimental researches of the I-steel column and beam-column joints,which are in complex stress state,based on portal frame structure under low cyclic loading.This paper analyzes the variation and characters of magnetic memory signal H_p(y)and tis gradient K of components’surface under various loads.The main works are as follows:(1)The basic theory of metal magnetic memory technology of ferromagnetic materials was analyzed,this technology is based on the magneto-mechanical effect principles of the ferromagnetic materials.Loads,which were applied to surface of ferromagnetic materials,can be equivalent to external magnetic field,thereby changing the structure of magnetic domain and the distribution of magnetic field,then self leakage magnetic field came into being,resulting the mutation of magnetic signals.Through the analysis of magnetic signals H_p(y)and its gradient K,magnetic field leakage intensity in the stress concentration and defects can be early detected.(2)Transverse detection line of web plate of steel I-column was analyzed,curves of H_p(y)of every detection line present different trends and shapes,results show that weak magnetic signals were influenced by various factors;Meanwhile they also present some laws and characteristics,such as asymmetry phenomenon,field reverse phenomenon,magnetization approach phenomenon,which were explained through J-A model theory.(3)The cross sections of the web plate mainly bear bending normal stress and shear stress,which are in complex stress state,but the stress is symmetric around the neutral axis of cross section,the value of stress is same,the direction is opposite,one side of cross section is tensile,the other side is compressed,according to the moment curve of the column and curves of H_p(y),the value of magnetic signals of tensile side is bigger than the compressed side,the value of two sides is same of the reflection point,which can be used to determine the tensile side and compressed side of steel components,meanwhile the reflection point can be characterized.(4)Vertical detection line of web plate and flage plate of steel I-column was analyzed,curves of H_p(y)and its corresponding gradient K of every detection line under different loads were draw.In the stress concentration area,the curves of H_p(y)would achieve extremum,the curves of K appear"zero"in the corresponding position and appear“peak-trough”phenomenon according to the curves of H_p(y)and K,which can determine stress concentration.(5)Vertical detection line of web plate and flage plate of steel I-column were analyzed contrastively,results show that,when the stress and external environment are basically same,but direction of detection differs by 90°,the curves of H_p(y)present symmetric phenomenon.(6)Detection dots of beam-column joints in near-end and far-end domains were analyzed,curves of H_p(y)of every detection line under different loads were draw,results show that the existence of oblique ribbed plates would increase the rigidity of beam-column joints,the stress that was applied to web plate would decrease,the value of H_p(y)of detection dots would less,which illustrates stress can make a big influence on magnetic memory signals of ferromagnetic materials.Transverse detection line of web plate was analyzed,the ecistence of ribbed plate and weld line can result mutation of magnetic memory signals in the same cross section.Through contrastive analysis of beam-column and steel I-column,some same laws and characteristics can be acquired,such as asymmetry phenomenon,magnetization approach phenomenon,some different laws were presented,which can illustrate the value and direction of stress,external ferromagnet and welds can produce collective effects on magnetic memory signals of ferromagnetic materials.