Validation of three dimensional eddy-current probe-flaw interaction model using analytical results

A volume element calculation has been used to predict the field at the slot in a conductor excited by an eddy current probe. The slot simulates the presence of a surface crack in a metal component. Interaction between the simulated flaw and the electromagnetic field is computed in order to model the fundamental physical process of eddy-current nondestructive evaluation. The results are used to suggest methods for improving testing techniques and to develop procedures for processing inspection data. As part of an ongoing program to validate the computer model, the authors compare predictions of the volume element calculation with analytical results for a test case. In the test problem, a constant, unidirectional eddy-current distribution is perturbed by a semicircular crack of negligible size at the surface of a half-space conductor. By taking the low-frequency limit, the field at the flaw and the change in probe impedance due to the presence of the flaw are given explicitly by simple analytical expressions. Numerical results found using the volume element calculation are compared with values found from the analysis, and good agreement is found