| Ferromagnetic materials,mainly iron and steel,are widely used in the manufacturing of bearing parts or structures in the industrial field,so it is necessary to detect and evaluate the stress of these materials.Among many non-destructive testing techniques,magnetic stress measurement method can reflect the stress concentration state and damage degree inside ferromagnetic materials through magnetic field signals on the surface of the material,so as to realize early diagnosis of the damage of components and the formation of defects.In this paper,by means of experimental research and numerical simulation,45#steel is taken as the research object to study the magneto-magnetic effect under weak AC excitation,and explore the variation rule of magnetic leakage signal on the surface of the sample,in order to achieve an effective and accurate assessment of the stress state of the component.(1)The basic theory of magneto-magnetic effect is briefly introduced in this paper,and the influencing factors of AC electromagnetic field,the magneto-magnetic effect under static tension and the evolution law of magnetic field under cyclic tensile stress are analyzed theoretically.The force-magnetic coupling model of stress-permeability is derived,which lays a foundation for the subsequent finite element simulation.(2)Firstly,the influence factors of weak AC excitation magnetic field were studied and analyzed to explore the influence of excitation frequency and lifting height on the detection signal.The finite element simulation results showed that under low frequency AC excitation and lifting height of 1 mm,the magnetic field signal was more accurate and clear;An experimental system was built to detect the magnetic field signals at the lifting height of 1 mm,2 mm,5 mm and 10 mm.The results showed that the magnetic field signals became weaker and weaker as the lifting height increased.(3)Both the finite element simulation results and the experimental results of the magneto-magnetic effect of ferromagnetic materials under static load tension show that the tangential component of the magnetic field has the maximum value at the stress concentration site and the normal component crosses the zero,which proves the applicability of the force-magnetic coupling model.Moreover,the tangential component of the magnetic leakage field of the specimen is negatively correlated with the stresspermeability model.On this basis,the quantitative correlation between static tensile stress and magnetic characteristic parameters is established in order to realize stress evaluation.(4)The finite element simulation and experimental study of cyclic tensile stress were carried out on the specimen.The simulation results show that,under the same number of cycles,when the stress amplitude increases from 50 MPa to 250 MPa,the residual stress in the specimen still forms a stress concentration area above the central circular hole,but the variation range of the magnetic leakage field signal of the specimen is small,and the normal component of the specimen does not change significantly.The cyclic stress with stress amplitude of 100 MPa-600 MPa is applied to the specimen.The experimental results show that with the increase of the number of cycles,the magnetic characteristic parameter value of the specimen leakage magnetic field will also increase,and the stress at each stage corresponds to a magnetic field saturation value.When the number of cycles reaches a certain degree,the magnetic field signal reaches a stable degree.Finally,the mean value method of magnetic signal characteristic parameters is used to establish the force-magnetic correlation under cyclic tensile stress.To sum up,this paper focuses on the study of AC electromagnetic field detection technology,mainly on the influencing factors of AC electromagnetic field,magnetic signal change rule under static load tensile,magnetic signal change rule under cyclic tensile stress and quantitative analysis of the forcemagnetic relationship. |
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