Research On Finite Element Analysis Of Eddy Current Testing Based On Domain Decomposition

Eddy current testing(ECT)is an important nondestructive testing technology for examining conductive materials.It has advantages of noncontact,single-side inspection,easy operation,easy realization of automatic testing,fast detection speed,etc,and has a wide range of applications in many fields.Numerical simulation of ECT is helpful for predicting and deeply understanding eddy current(EC)signals,designing new probe,optimizing parameters,quantifying and reconstructing defects,training testing personnel,and scientifically guiding the study of ECT.Therefore,it is of great significance to study the numerical simulation of ECT.In this thesis,research on finite element(FE)analysis of ECT is carried out,and the main contents are as follows.The FE analysis of pulsed eddy current testing(PECT)for linear isotropic materials is studied.The FE model for PECT of linear isotropic materials with ferrite-core coil is established.The FORTRAN language is used to write computer programs to simulate the PECT with scanning of ferrite-core coil.The domain decomposition method and the frequency spectrum interpolation method are used to calculate the response signals of PECT,which avoids the problem of re-meshing during probe scanning,decreases the mesh scale,reduces the difficulty of simulation,greatly reduces the amount of calculation,and significantly improves the calculation efficiency.The simulation results are verified by experiments.The agreement of the experimental and the simulation results demonstrates the correctness of the simulation results.The FE analysis of ECT for linear anisotropic materials is studied.Based on the vertical EC method,a bridge-type vertical EC probe composed of coplanar dual rectangular coils with magnetic cores and bridge circuit is designed.The domain decomposition finite element method(FEM)is used to simulate the ECT of carbon fiber reinforced polymer(CFRP)with the bridge-type vertical EC probe.According to the simulation results,delaminations of different thicknesses,depths,and areas in CFRP can be identified,and the ranges of delaminations can be obtained.Then experiments are carried out using the bridge-type vertical EC probe.Like the simulation results,the experimental results show that delaminations of different thicknesses,depths,and areas in CFRP can be identified and the ranges of delaminations can be obtained.The experimental results are compared with the simulation results,and they are verified by each other.The FE analysis of ECT for linear isotropic materials is studied.A hybrid formulation domain decomposition FEM is presented for the simulation of ECT with scanning of ferrite-core coil.The solution domain is decomposed into two subdomains,and the test sample and the ferrite core are included in different subdomains.The subdomains are discretized independently.Different mathematical formulations are used in different subdomains when solving the problem of ECT.In the example of this thesis,the Ar,V-Ar formulation is utilized in the subdomain of the test sample in which EC is induced,and the φ formulation is used in the subdomain of the ferrite core where there is no EC.The hybrid formulation method is used to simulate ECT of aluminum plates.Compared with the unitary formulation method where the Ar,V-Ar formulation is utilized in both subdomains,the hybrid formulation method has fewer unknowns and higher computational efficiency.Experiments are carried out and the results are consistent with the simulation results,which verifies the correctness of the numerical method.