An efficient method for output prediction of a surface eddy current probe in the presence of an axial fatigue crack in a conducting cylindrical rod

Abstract

This paper proposes an efficient method for analyzing the output signal of a surface eddy current probe during scanning a fatigue crack in a conductive cylindrical test specimen. The proposed method addresses all facets of typical eddy current testing practice, accounting for variations in metal conductivity and permeability, the arbitrary shape of the excitation coil and operating frequency. In this method, we initially employ the equivalence theorem to replace the crack opening with equivalent magnetic and electric current densities. Then, using appropriate dyadic Green's functions, the governing volume integral equations (VIEs) are formulated. Finally, the method of moments is utilized to solve the VIEs. This is done by expanding the unknown current densities in terms of dully selected basis functions of compatible with the problem, and hence, reducing the integral equations to a matrix equation. It is shown that the diffusion characteristics of the electromagnetic field in conductors enables one to adopt entire domain basis functions of polynomial form that remarkably reduces the computation burden in the formation of the resultant matrix equation. The validity and computational efficiency of the proposed method are verified through comparison of simulation results with experimental data and those obtained using a commercially available finite-element code.