Semi-analytical simulation of eddy current testing signals due to narrow cracks embedded in a multilayered planar medium
Résumé
Fast and accurate simulation of eddy current testing (ECT) of thin cracks in conductive pieces using standard numerical or semi-analytical volumetric models is still a matter of concern nowadays, due to the small --compared to the skin depth-- dimension of the cracks in their opening direction. The formalism of the boundary elements method (BEM) has been proposed in the literature to treat the case of an ideal crack. A recent improvement on this method carries out the evaluation of the dyadic Green function analytically in the spatial domain by using the well-known Sommerfeld identity combined with the Generalized Pencil Of Function method (GPOF). This approach has shown to considerably improve the performance in terms of computation time since the fill-time of the moment matrix involved is drastically reduced, a very good degree of precision being still achieved. Starting from these results obtained in the case of a plate, a collaborative work by the authors has been started that aims at developing a quite general semi-analytical model dedicated to the simulation of ECT signals that are due to multiple thin cracks embedded in multilayered planar structures. Two developments are presented in this contribution: the medium containing the crack is first generalized to a non-magnetic multilayered structure. The global performance of the model appears very satisfactory in comparison to volumetric models, as only the flawed region needs to be meshed in two dimensions. Synthetic results obtained in so doing are compared to measurements from well-known benchmark cases as well as to numerical results obtained with volumetric models. The modelling of problems involving multiple cracks in a planar layered medium is also introduced. First results, as well as further improvements of the model currently in progress, are discussed.