Research On Eddy Current Detection And Evaluation Method For Surface Defects Of Traction Motor Shaft Based On Finite Element Method

As an important bearing part of the locomotive drive mechanism,whether the traction motor shaft has a good working condition is closely related to whether the train can run safely.If the shaft fails due to defects,people’s lives and property safety will be threatened.Therefore,it is very necessary to timely identify and quantitatively evaluate the surface defects of the traction motor shaft.There are still difficulties in the quantitative evaluation of defects by traditional eddy current testing,and the traditional method of calculation and analysis based on coil impedance is gradually unable to meet the development needs of nondestructive testing.For this reason,unlike the previous impedance analysis methods,this paper takes the magnetic field with rich characteristic information as the starting point,and through finite element analysis,fully explores the response law of the electromagnetic field.The main research contents of this paper are as follows:(1)The eddy current detection models of the traction motor shaft under different coil turns,excitation current frequency,excitation current amplitude and lift-off value were established,and the influence of system parameters on eddy current detection was revealed.It provides a reference and basis for improving detection sensitivity and accuracy.It is found that good detection results can be obtained when the number of coil turns is 500;the smaller the frequency of the excitation current,the larger the amplitude of the excitation current,and the smaller the lift-off value,the easier it is to detect the defect signal.(2)The eddy current detection models of the traction motor shaft with different geometric parameters and shapes were established,the relationship between the geometric size,position,shape and other parameters of the defect and the electromagnetic characteristics were analyzed,and the feature quantity representing the defect was extracted to realize the detection and quantitative evaluation of the defect.The accuracy of the simulation data is verified by experiments.By studying the curve changes of the horizontal magnetic induction intensity B_x and its phaseφ_x,the vertical magnetic induction intensity B_y and its phaseφ_y,the results show that B_x,B_y,andφ_x can qualitatively and quantitatively evaluate the crack width,qualitatively evaluate the crack depth and hidden depth.The characteristic peak distance in the B_x change curve,the characteristic peak distance in the B_y change curve,and the hysteresis interval in theφ_x change curve can realize quantitative evaluation of defects.φ_y is insensitive to crack width,depth and hidden depth,and cannot qualitatively or quantitatively evaluate defects.The study also found that the crack defect at the axicon is similar to the magnetic field response law of the crack defect at the plain shaft,but there will be a phenomenon of"high on the left and low on the right".In addition,by revealing the magnetic field response laws of cylindrical hole and conical hole defects under different parameters,it is verified that B_x,B_y,andφ_x can effectively evaluate the transverse width and longitudinal depth of defects.(3)The eddy current detection probe models with different geometric structure parameters were established,and the influence of the coil geometric structure parameters on the resolution of the sensor was explored.The results show that at a closer position,increasing the difference between the inner and outer radii,reducing the thickness of the coil,and reducing the equivalent radius of the coil are beneficial to improving the resolution of the probe coil;at a farther position,reducing the difference between the inner and outer radii,increasing the thickness of the coil,and reducing the equivalent radius of the coil are beneficial to improving the resolution of the probe coil.The accuracy of the simulation data is verified by comparing the simulation results with the theoretical values under different geometric structure parameters,which provides ideas for the structure optimization of the probe coil.