Experimental Study On Force-Magnetic Relationship Of Steel Specimens Based On Metal Magnetic Memory

Metal magnetic memory testing?MMMT?can be a new non-destructive testing technology for early diagnosis of ferromagnetic materials,which uses the magnetic field as the excitation magnetic field.At present,there is still a lack of thorough research on the quantitative evaluation of stress concentration by this technology,and the lack of research on weak magnetic materials.Stainless steel materials such as austenitic stainless steel itself do not have magnetic properties,but a certain amount of magnetic properties will be generated after cold-working deformation.Therefore,the research on force-magnetic relationship will be carrying out by combining simulation,experimental research and theoretical analysis,which based on the correlation knowledge of metal magnetic memory testing technology was applied to low carbon steel Q345B,Q235 and stainless steel materials?austenitic stainless steel304 and ferritic stainless steel 430?in this thesis.Taking the Q345B plate specimens with central diameter hole as the research object,simulate the magnetomechanical coupling of the plate specimens.The simulation result shows that the magnetic memory signal curve decreases from positive to negative,and there is a zero-crossing phenomenon in the stress concentration part,and nonlinear changes occur,and the maximum of the magnetic field gradient value appears.At the same time,the static load tensile test were applied to the plate specimens with the different diameters of the hole,and the surface leakage magnetic field of the unloaded plate specimens was detected,then mapping and comparative analysis according to the measurement result.Which shows that three-dimensional map of the magnetic memory signal gradient value K changes on the tress concentration area;In addition,when measuring the leakage magnetic field around the circumference of the circular hole,it is found that the diameter of the circular hole is related to the demagnetization factor,which indirectly affects the strength of the surface leakage magnetic field.And which will provide support for the further research and development of magnetic memory testing technology.Taking the Q235 plate specimen with the central hole as the research object,the influence of the environmental magnetic field on the relationship of stress and magnetic of the ferromagnetic material is studied.The result shows that in the geomagnetic environment,the magnetic memory signal curve is approximated to horizontal line without any applied load;when applying the external load,in a certain range of the applied external magnetic field,when the direction of the external magnetic field is consistent with the direction of the geomagnetic field,the external magnetic field is positively correlated with the magnetic memory signal;when the direction of the external magnetic field is opposite to the direction of the geomagnetic field,the external magnetic field is negative correlation with magnetic memory signal.The larger the applied external magnetic field,the more obvious the magneto-mechanical effect in the stress concentration area.Then the research on the interference factors of magnetic is realized.Taking stainless steel?austenitic stainless steel 304 and ferritic stainless steel 430?as the research object,the static tensile tests of specimens with different notch types?semicircular-notch,V-notch,double-associated notch?was carried out.The result shows that the magnetic memory signal curve of austenitic stainless steel is horizontally wavy,while the magnetic memory signal curve of ferritic stainless steel is inclined from low to high.For the stress concentration area,the magnetic memory signal curve mutations and the phenomenon of the magnetic memory signal value zero occurs.With the increase of the stress,firstly the characteristic parametersH_max-H_minmeasured on austenitic stainless steel maintains the level,and then begins to increase rapidly;m_maxshows a“n”shape change trend,which can reflect the change law of elastic-plastic stage well.For the common ferritic stainless steel 430,the curve change of the s?k?,H_max-H_minandk_medis the most obvious,both of them increase firstly and then maintain the level with the increase of the stress,and provide evidence for MMMT of stainless steel materials for the after-utilization of related parameters and the changes of signal curve.