Ferrous Material Stress Test And Evaluation Based On Magnetic Domain And Macro Magnetic Properties

Stress affects the durability and the service life of the components.Barkhausen noise technique is an effective electromagnetic nondestructive stress detection technique.The discontinuous movement of magnetic domains generates Bakhausen noise.The microstructure and stress of the material affect the magnetic domain distribution and the moving behavior of the magnetic domain,which significantly affect the Barkhausen noise signal.However,the current stress detection methods based on Barkhausen noise lack the establishment of a physical mapping model of material microstructure and macro magnetic characteristics,which makes it difficult to investigate the effect of microstructure on stress nondestructive test and evaluation.Therefore,it is of great significance to establish physical models of material microstructure,micromagnetic signals,and magnetic Barkhausen noise for stress nondestructive test and evaluation.To explore the problems above,based on magneto-optic Kerr microscope imaging system and magnetic Barkhausen noise detector,the physical mapping model of domain wall movement and Barkhausen noise is established.Then,the temporal and spatial characteristics of domain wall movement and magnetic Barkhausen noise under stress are quantified.After that,the influence of material microstructure on magnetic domain and magnetic Barkhasen noise is analyzed to stress detection and evaluation in elastic and plastic range of ferromagnetic materials by using magnetic Barkhausen noise.The main contents and innovations are summarized as follows:(1)Magneto-optical Kerr microscope imaging system is established to characterize the domain wall movement inside grain and around grain boundary under tensile stress.The difference in the distribution and dynamic behavior of domain walls at different positions is due to the difference in magneto-elastic energy at different positions under stress.The magnetization work quantitatively analyzes the difference of the domain wall movement under different stress inside the grain and around the grain boundary.The difference of magnetization work on different locations is highly affected by stress in the elastic range.The results provide a theoretical basis to analyze the influence of material microstructure inhomogeneity on stress detection and evaluation by using magnetic Barkhausen noise.(2)Based on the observation of time characteristic of domain wall motion,the time response inhomogeneity of magnetic Barkhausen noise inside and around grain boundaries during elastic deformation of ferromagnetic materials is analyzed at the micro-scale.The time response histogram of magnetic Barkhausen noise is proposed to show the different time characteristics of domain wall movement on different locations during elastic deformation.According to the time response of domain wall movement at different positions,time-division is carried out to extract root-mean-square(RMS),mean,and peak in the optimized time interval to separate the variation of magnetic properties affected by the grain and grain boundary under low tensile stress.(3)Based on the observation of domain wall motion and magnetic Barkhausen noise,a correlation model of domain wall motion velocity and magnetic Barkhausen noise envelope under stress is established.The correlation between RMS,mean value,and peak value of magnetic Barkhausen noise signal and domain wall motion velocity of silicon steel sheet under tensile stress is analyzed.The tensile stress increases the 180°domain walls of ferromagnetic materials and reduces the coercive force field,thus increasing the velocity of the domain walls and the magnetic Barhausen signal.The correlation between domain wall velocity and magnetic Barkhausen signal is higher than 96%.It provides a theoretical basis for the subsequent Barkhausen noise transient model establishment to analyze the stress state under elastic and plastic deformation.(4)Barkhausen noise transient model is established to analyze the evolution of microstructure during elastic and plastic deformation.With the observation of domain wall distribution and microstructure,the correlation between material microstructure and MBN transient model is investigated to verify the ability of stress detection and evaluation on the microscopic scale.The positive and negative correlations between Barkhausen noise transient models and stress characterize the evolution of microstructure during elastic and plastic deformation.The fusion of the duration and intensity(,)of the Barkhausen noise transient model distinguishes the stress states in the elastic and plastic ranges at the microscopic scale.Under stress in the plastic range,grain boundary migration and dislocation appear which make the transient model of Barhausen noise appear non-homogeneity on grain boundary and grain.Grain boundaries become more unstable under the action of stress.Barkhausen noise transient model has enough ability to evaluate stress of Q235 sheet and silicon steel sheet during elastic and plastic deformation.The above study analyzes the spatial and temporal relationship of micro-macro magnetic signals to evaluate the stress of ferromagnetic materials,which provided a theoretical basis for the development of new high-spatial and high-temporal magnetic signals for stress nondestructive test and evaluation.