A Perturbation Technique for the Finite Element Modelling of Differential Probes in Nondestructive Eddy Current Testing

Abstract:
The ultimate goal of nondestructive eddy-current testing (ECT) problems is to determine the position and size of defects in conducting materials (inverse problem). However, a fast and accurate calculation of the probe response (forward problem) is often required for identifying the flaws from measured data. Several variations of the volume integral method (VIM) have been reported in literature for solving this kind of problems. Nevertheless, these techniques become extremely expensive in case of more complicated geometries other than infinite stabs or tubes. The finite element method allows to overcome these drawbacks. However, it may require a dense discretisation in the vicinity of the defect resulting in a large 3D mesh. Further, calculations for different probe positions are performed independently, which is time consuming. This paper deals with an extension of the method for taking into account differential probes and multiply connected test pieces. As test case, a tube with a crack and a differential probe that scans its outer surface is considered.