Study On Measurement Of Electrical Conductivity Of Metals Based On Eddy-current Method

Quality control of metal materials is critical to the design performance of mechanical components.Conductivity is one of the important physical quantities to characterize the mechanical properties of metal materials.It is closely related to metal composition,internal stress state,aging,heat treatment state,hardness and metal microstructure.The eddy current method based on the principle of electromagnetic induction has the advantages of high speed,low cost,non-destructive,non-contact,etc.,and is widely used for conductivity detection of metal materials.Based on the eddy current finite element theory,the finite element model is established by Ansys Maxwell,and the simulation study of conductivity detection is carried out.A new method for non-ferromagnetic and ferromagnetic metal conductivity detection is proposed,from the aspects of detection accuracy,sensitivity and resolution.The performance of the new method was evaluated.The main research contents and innovations of this paper are as follows:(1)Based on Maxwell's equations and electromagnetic field finite element theory,the finite element model of conductivity eddy current testing was established by Ansys Maxwell software.The simulation results of analytic model and finite element model were compared to verify the correctness of the finite element model.(2)Using the finite element model to simulate the relationship between the probe impedance and the conductivity of the test piece,it is found that there is a good linear relationship between the logarithm of the phase signal of the coil impedance change and the logarithm of the conductivity;a conductivity detection method is proposed.The influence of the lift-off and excitation frequency on the detection signal was studied.According to this,the probe was placed on the test piece to remove the impedance of 1mm instead of the impedance in the air as the reference signal to suppress the lift-off effect.(3)Investigate the influence of parameters such as conductivity interval,specimen size and specimen radius of curvature on conductivity detection method,and evaluate the detection accuracy,sensitivity and resolution from both quantitative and qualitative points.The minimum size of the piece is proposed.The conductivity correction method of the nonflat test piece based on curvature is proposed,and the range and theoretical precision of the conductivity detection method are quantified.(4)The sweep eddy current signal of ferromagnetic material conductivity and permeability is studied.The signal analysis shows that the peak frequency of the normalized reactance change does not change with the permeability,only related to the conductivity,according to which,success Decoupling the eddy current signals of conductivity and permeability,the conductivity measurement method of ferromagnetic materials based on the peak frequency of normalized reactance variation is proposed.Experiments show that the detection accuracy is within 4%,and the effectiveness of the method is verified.The research results in this paper provide a new detection method for the conductivity detection of metal materials,and point out the next research direction,which has important theoretical and practical value.