Numerical and Experimental Study of Eddy Current Crack Detection around Fasteners in Multi-Layer Structures

IET Science Measure & Tech

Reboud

2021

This paper proposes a non-iterative procedure for flaw(s) characterization based on Pulsed Eddy Current Testing (PECT) signals analysis. The adopted inversion strategy is based on the use of supervised statistical learning algorithms. A numerical forward solver, based on the Finite Integration Technique (FIT), is used for the generation of the training data (the input-targets couples of the learning algorithm). Predictions are then carried out in almost real-time using a non-linear kernel based regression method, known as kernel ridge regression. It turns out that the direct fit of the regression model to the raw PECT signals may lead to poor prediction accuracy due to the large cardinality of PECT signals. To remedy this problem, an adaptive sampling strategy has been adopted in this work. The performance of the proposed methodology is discussed and compared with solutions proposed in the literature.

Section: Introductionmentioning

confidence: 99%

Flaw characterization in conductive media based on pulsed Eddy current measurements: A fast non‐iterative inversion approach

Miorelli

IET Science Measure & Tech

Reboud

2021

“…Therefore, the straightforward application of the integral equation approach for the flaw response calculation in the vicinity of boreholes is to treat the hole itself as a supplementary defect of the geometry and apply the integral formalism to the plate for which both the primary field and Green's dyad expressions are well established [3]- [6]. A more elaborate approach consists in treating the plate-borehole ensemble as a single piece, which, however, necessitates the development of solutions for both the primary field and Green's dyad.…”

Section: Introductionmentioning

confidence: 99%

Calculation of the Eddy-Current Flow Around a Cylindrical Through-Hole in a Finite-Thickness Plate

Theodoulidis

2015

IEEE Trans. Magn.

A semianalytical solution to the eddy-current induction problem in a conducting, nonmagnetic plate near a cylindrical through-hole is derived by means of the second-order vector potential and the domain truncation technique. The construction of a solution, which simultaneously satisfies the field continuity across the cylindrical surface of the hole and the planar interfaces of the plate, proves to be a very challenging problem, and thus, a special superposition of partial subsolutions is proposed. The presented solution is part of a more general development aiming at the calculation of the probe interaction with material flaws located in the vicinity of the hole by means of the integral equation formalism. These tasks will be the subject of a future paper. The comparison of the semianalytical results against both finite-element simulations as well as experimental data demonstrates excellent agreement.Index Terms-Domain truncation, eddy-current testing (ECT), fastener inspection, impedance calculation, mode matching. 0018-9464

“…To the best of the authors' knowledge, the state of the art concerning the calculation of crack signals in the proximity of the borehole/fastener edge consists either of the brute meshing of the whole region via FEM or of the application of the volume integral method (VIM), where both crack and hole are considered as 'flaws', and they are discretized simultaneously using Green's function of infinite planar multi-layered media (Knopp et al 2004(Knopp et al , 2006(Knopp et al , 2009Reboud et al 2010). The perspective of this work faces the alternative of applying the boundary element method (BEM) on the crack surface only.…”

Section: Introductionmentioning

confidence: 99%

Solution to the eddy-current induction problem in a conducting half-space with a vertical cylindrical borehole

Theodoulidis

2012

Proc. R. Soc. A.

The eddy-current induction problem in a conducting half-space with a vertical borehole is studied and a solution based on modal techniques is presented. Owing to the particular characteristics of the specific geometry, the straightforward application of the truncated region eigenfunction expansion method (a well-established tool for the analytical solution of such problems) presents significant difficulties. Therefore, a modified truncation approach has been adopted that treats the problem in two steps, each one based on the superposition principle. The approach proves to be very efficient and numerically robust. Results for the coil impedance are in excellent agreement with those obtained with the finite-element method. From the engineering point of view, the geometry simulates the eddy-current inspection of fastener holes in aircraft structures when coil scanning is performed from the surface. The presented solution constitutes an important step towards the development of a complete model for fastener hole crack inspections.