An effective 3-D finite element scheme for computing electromagnetic field distortions due to defects in eddy-current nondestructive evaluation

A new three-dimensional (3-D) finite element scheme for eddy-current nondestructive evaluation (NDE) problems is described that calculates directly the perturbation of the electromagnetic field due to defects in metallic specimens. The computational costs of such problems are usually very high using available finite element schemes, and the new scheme is supposed to lower these costs. The basic concept, the direct calculation of the field distortion due to the flaw, is provided for rather general defects, but the detailed finite element scheme is discussed for zero-conductivity flaws. The source terms of the formulation are determined from the unperturbed field, and the impedance change due to a defect can be calculated as an integral over the flaw. A finite element scheme for solving problems with crack-type defects is also presented as a limiting case of the formulation for zero-conductivity flaws. Solutions of a benchmark problem from the testing electromagnetic analysis methods (TEAM) workshop series (problem number 15/2) and of tube problems with artificial slots are presented and compared to experimental data