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Eddy curent modelling for nondestructive testing



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V. Maillot, G. Pichenot, F. Buvat, H. Voillaume,

16ème conférence mondiale sur les contrôles non destructifs, Montréal, 30 août-3 septembre 2004,

Rapport DSR 31


Eddy current nondestructive evaluation is widely used to inspect conducting materials during manufacture or in service. In this context, modeling is a powerful tool for inspection improvements : it helps probe-coil designers to optimise sensors for each examination requirement, it gives better understanding of the involved physics, it helps operator training and it also increases defect analysis reliability. This contribution presents the recent progresses in developing models which have the capability to predict quickly the signal of an eddy current probe used in nondestructive testing. These codes form a part of the tools available in CIVA which is a multi-technique (ultrasonic, radiographic, electromagnetic) platform for NDT. It is shown how these models, included in the convivial user interface of CIVA, can be used in order to optimize the design of probe-coils and study various configurations of control. It is a powerful tool for implementation of industrial NDT methods (e.g. coil shape, frequencies) and evaluation of perturbation parameters (e.g. lift-off, tilt) by limiting the number of experimental tests. This paper tackles the various analytical and semi-analytical approaches used in these models. In particular, it presents simulations of the response of eddy current probes due to a 3D flaw located in a plate or in a tube, obtained with models based on dyadic Green function calculations in the framework of the volume integral formalism. The case of testing with a ferrite core probes is also detailed. All models developed and integrated in CIVA have been validated using experimental results.