Quantitative Evaluation Of Stress Of Oriented Electrical Steel Sheet Based On Magnetic Barkhausen Noise Energy Loop

Oriented electrical steel,as a soft magnetic material with excellent electromagnetic properties,is widely used in the manufacture of all kinds of transformer cores.Due to the magnetostriction of transformer laminate core,structural bending effect and stacking in assembly,the electrical steel sheet will be subjected to extrusion or tensile stress.Mechanical stress can significantly change the magnetization and loss characteristics of oriented electrical steel sheet,thus affecting the working efficiency and operation characteristics of transformer.Quantitative evaluation of the stress of oriented electrical steel sheet is of great significance for the fine design of power transformer and the improvement of the operation efficiency of the equipment.Magnetic Barkhausen Noise(MBN)is a high frequency electromagnetic signal generated when the domain walls of ferromagnetic materials move through pinning sites under the excitation of external magnetic field.It is very sensitive to the change of stress state,microstructure and composition of ferromagnetic materials,and is widely used in nondestructive testing of ferromagnetic materials.Firstly,a method of constructing magnetic Barkhausen noise energy loop MBNE(H)from original MBN signal is proposed.Based on the physical mechanism of MBN,the proportional relationship between the energy loss and the voltage signal VB of MBN is established,and it is related to the energy loss through wall pinning in the Jiles-Atherton hysteresis model.A novel magnetic Barkhausen noise energy eigenvalue(MBNE)is defined by the time integral of the product of the absolute value of VB and the sign function sign(dH/dt),which is proportional to the irreversible magnetization Mirr.Because Mirr is equal to the saturation magnetization Ms when the magnetization of the ferromagnetic material reaches saturation,the MBNE can be scaled proportionally so that the maximum value is equal to Ms,and the functional image of MBNE with respect to the magnetic field intensity H is drawn.The obtained MBNE(H)is called the magnetic Barkhausen noise energy loop.The rescaled MBNE(H)coincides with the irreversible hysteresis loop Mirr(H).Then,the MBNE(H)of oriented electrical steel sheet under no stress,tensile stress and compressive stress is tested and compared with Mirr(H),which verifies the effectiveness of MBNE(H)construction method.The method of extracting Mirr(H)from the original signal of MBN reveals the relationship between the physical mechanism of MBN and the irreversible magnetization process of magnetic materials.At last,based on the extended magnetomechanical hysteresis model,the linear relationship between the reciprocal of the differential susceptibility of MBNE(H)coercive point and the stress is derived,and a linear calibration curve which can be used to quantitatively evaluate the stress is given.In order to verify the correctness of the theoretical formula,the differential magnetic susceptibility of MBNE(H)coercive point of oriented electrical steel sheet under different elastic tensile stress and compressive stress was measured.The experimental results are in good agreement with the theoretical calculation results,which provides a simple and practical method for quantitative evaluation of mechanical stress of oriented electrical steel sheets.In practical application,only by measuring the MBN of silicon steel sheet and obtaining the differential magnetic susceptibility of MBNE(H)coercive point,the corresponding stress can be found on the calibration curve.Compared with other stress detection methods,this method has the advantages of low cost and high efficiency.