Research On Magnetic Memory Characterization Of Q235 Steel Bending Deformation Damage

Carbon structural steel as a common ferromagnetic material is widely used in all kinds of light and heavy industry.However,As a component of force,it will cause early damage and lead to serious accidents such as failure,fracture and explosion due to various types of impact and load.Therefore,it is very important to use the efficient nondestructive testing methods and pre-evaluation technology for the early detection.Metal magnetic memory technology,as a new nondestructive testing technology,can not only detect the plastic deformation and macro defects of metal materials,but also detect the early stress concentration of ferromagnetic materials.It is necessary to research on magnetic memory testing technology of carbon structural steel in many methods and with several relevant parameters.Therefore,in this paper,the Q235 rectangular beam steel specimen is taken as the research object.The three-point bending test is carried out on the specimen without defects and specimen of V-notch defects.And the strain signal in the loading process and the magnetic memory signal after loading are collected,summed up distribution characteristics of normal and tangential component of magnetic field of the steel surface in the elastic stage after removed load,and analyzed the relation between magnetic field and elastic stress.The relationship between magnetic memory signal and strain was analyzed by means of statistics.Finally,the statistical results were verified by defects of U-notch test pieces.Testing results show that there exists an inevitable connection between the two components of the surface magnetic field and the elastic stress,if there is obvious defect or stress concentration in the specimen,the tangential component of magnetic memory signal Hp(x)will have a strong response that the value of Hp(x)is positively correlated with the change of the load.As specimens under bending load are separated from the load,there is a"memory" on the surface of the specimen that the state of stress previously attained,and the position of defect of the specimen surface can be determined by the memory of the magnetic field signal.Along the direction of signal acquisition,the tangential component of magnetic field Hp(x)presents a state that peaks and troughs at both sides of the stress concentration position.Normal component of magnetic field Hp(y)is reversed at both sides of the stress concentration position.In this paper,the correlation between magnetic field signal and strain signal is analyzed.If there are no significant defects in the component,only the shear strain is highly correlated with the magnetic memory signal.If horizontal,vertical and shear strains are taken together,it can strongly influence the magnetic memory signal and establish a simple linear model between the comprehensive strain and magnetic field.If there are significant defects in the component,the magnetic memory signal is not directly affected by the strain in one direction,and the comprehensive strain can not directly affect and act on the magnetic memory signal.As an important parameter introduced in this article,relative magnetic field index re-established the relationship between the integrated strain and magnetic memory signals.There is a high linear correlation between the comprehensive strain with the relative tangential magnetic field index and the tangential magnetic memory signal in defective specimen after bending deformation.In this paper,the research on the bending damage of Q235 steel mainly focuses on the distribution of magnetic memory signals and the relationship between magnetic memory signals and strain.The conclusions drawn are of certain accuracy and feasibility.