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Eddy-current probe impedance due to a volumetric flaw

1991; American Institute of Physics; Volume: 70; Issue: 3 Linguagem: Inglês

10.1063/1.349615

1520-8850

John R. Bowler, S.A. Jenkins, L. David Sabbagh, H.A. Sabbagh,

Welding Techniques and Residual Stresses

Eddy current induced in a metal by a coil carrying an alternating current may be perturbed by the presence of any macroscopic defects in the material, such as cracks, surface indentations, or inclusions. In eddy-current nondestructive evaluation, defects are commonly sensed by a change of the coil impedance resulting from perturbations in the electromagnetic field. This paper describes theoretical predictions of eddy-current probe responses for surface cracks with finite opening. The theory expresses the electromagnetic field scattered by a three-dimensional flaw as a volume integral with a dyadic kernel. Probe signals are found by first solving an integral equation for the field at the flaw. The field equation is approximated by a discrete form using the moment method and a numerical solution found using conjugate gradients. The change in probe impedance due to a flaw is calculated from the flaw field. Predictions of the theory are compared with experimental impedances due to eddy-current interaction with a rectangular surface breaking slot. Good agreement is found between predictions and the measurements.