Calculation of the ECT signal of a minute crack by a FEM-BIM hybrid method

Abstract

A hybrid method is presented for the calculation of the interaction of a complicated shape ferrite-core eddy current testing probe with extremely small size cracks in a plate. The method is obtained by blending the boundary integral (BIM) and finite element (FEM) methods preserving their attractive properties, that is, the fast and accurate evaluation of the defect field and the versatility in specimen and probe geometry, respectively. FEM is applied for the computation of the electric field induced in the specimen without cracks. Using the obtained, so-called, incident field the BIM is used for the calculation of the field perturbation due to the presence of the cracks in the tested specimen. With the application of the presented hybrid calculations, a very fast and accurate method is developed for the solution of a problem that would pose considerable difficulties for either the FEM or the BIM if they were applied purely alone in the conventional way. The results of the calculations are compared with a large number of experimental data. The very good correlation between the measured and simulated probe responses proves the applicability of the presented method.