Thin-skin eddy-current interaction with semielliptical and epicyclic cracks

Bowler, John R.; Harfield, N.

doi:10.1109/20.822538

Cited by 25 publications

(9 citation statements)

References 14 publications

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“…It can be seen from (14) and (16) that (10) is not satisfied exactly but is approximated by neglecting ψ 2 in the integral. Because ψ 2 is small compared with ψ 1 and the integral term is itself relatively small, the approximation is reasonable as can be corroborated from the comparison of direct problem predictions with experiment [11].…”

Section: Approachmentioning

confidence: 55%

Thin-skin eddy-current inversion for the determination of crack shapes

Bowler

2002

Inverse Problems

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An important aim of nondestructive evaluation is to quantify flaws in components using sensor measurements. In pursuit of this aim, a method has been developed for finding the size and shape of planar cracks in electrical conductors from single-frequency eddy-current probe impedance measurements. In the direct problem, the change in the impedance of an eddycurrent probe due to a crack in a conductor is determined in the regime where the skin depth is much smaller than the dimensions of the crack face. The thin-skin field at the crack face is represented by a potential satisfying the two-dimensional Laplace equation. In the corresponding inverse problem, the crack shape is sought from probe impedance measurements. Here the crack boundary is located using an iterative inversion scheme in which a cost function quantifying the overall difference between predictions and measurements is minimized using a gradient method. The gradient is found from the derivative of the cost function with respect to a variation of the flaw. Shape estimates found by the inversion of impedance data have been compared with the measured profiles of simulated cracks in aluminium plates. The comparisons show that the inversion scheme gives good agreement with direct physical measurements.

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Section: Approachmentioning

confidence: 55%

Thin-skin eddy-current inversion for the determination of crack shapes

Bowler

2002

Inverse Problems

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“…The first group is based on numerical methods such as the finite element method (FEM) (Biro and Richeter, 1991) or the volume integral method (VIM) which provide very accurate results but also require an expensive computational effort. In this group a very important place is occupied by the integral methods like boundary element method (BEM) for simulations of eddy current inspections of defects having negligible or narrow opening (Bowler, 1994;Bowler et al, 1994;Bowler and Harfield, 2000). A second group comprises analytical models, mainly for 2D cases, which are generally based on assumptions regarding the symmetry of the considered models (Dodd and Deeds, 1968;Theodoulidis and Kriezis, 2006).…”

Section: Ect Methodsmentioning

confidence: 99%

Space mapping methodology for defect recognition in eddy current testing – type NDT

Putek

Crevecoeur

Slodička

et al. 2012

COMPEL - The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

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Purpose -The purpose of this paper is to solve an inverse problem of structure recognition arising in eddy current testing (ECT) -type NDT. For this purpose, the space mapping (SM) technique with an extraction based on the Gauss-Newton algorithm with Tikhonov regularization is applied. Design/methodology/approach -The aim is to have a computationally fast recognition procedure of defects since the monitoring results in a large amount of data points that need to be analyzed by 3D eddy current model. According to the SM optimization, the finite element method (FEM) is used as a fine model, while the model based on an integral method such as the volume integral method (VIM) serves as a coarse model. This approach, being an example of a two-level optimization method, allows shifting the optimization load from a time consuming and accurate model to the less precise but faster coarse surrogate. Findings -The application of this method enables shortening of the evaluation time that is required to provide the proper parameter estimation of surface defects. Research limitations/implications -In this work only the specific kinds of surface defects were considered. Therefore, the reconstruction of arbitrary shapes of defects when using real measurement data from ECT system can be treated in further research. Originality/value -The paper investigated the eddy current inverse problem. According to aggressive space mapping method, a suitable coarse model is needed. In this case, for the purpose of 3D defect reconstruction, the reduced VIM approach was applied. From a practical view point, the authors demonstrated that the two-level inversion procedures allow saving of up to 50 percent CPU time in comparison with the optimization by means of regularized Gauss-Newton algorithm in the same FE model.

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“…In addition, The crack is assumed to have constant depth b and width . The results derived by Harfield and Bowler [31][32][33] can be used to derive the results for the tag's impedance.…”

Section: A Sensing Principles With Varying Temperaturementioning

confidence: 99%

Temperature Independent Defect Monitoring Using Passive Wireless RFID Sensing System

et al. 2019

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A significant requirement of low-cost sensing systems for defect detection is essential to bridge the gap of non-destructive testing & evaluation (NDT&E) and structural health monitoring (SHM). In practical situation, the temperature variation will be unknown in a priori and hence will give rise to uncertainty and unreliability in the defect detection. This paper demonstrates the potential use of low frequency (LF) RFID tag antenna based wireless sensors to characterise corrosion and crack progression in high-temperature conditions for potential structural monitoring. Consideration of the parasitic parameters which depend on the temperature variation is presented. The key factors that influences the sensing accuracy with regards to different materials due to inhomogeneity are presented. A cost-effective self-compensation method is proposed by means of a self-swept frequency measurement through selection and fusion of temperature dependent feature near the tag's resonance region. The experimental work validates the effectiveness of the method in temperature compensation and some initial results demonstrate the efficiency of the technique to overcome the inhomogeneity.

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Thin-skin eddy-current interaction with semielliptical and epicyclic cracks

Cited by 25 publications

References 14 publications

Thin-skin eddy-current inversion for the determination of crack shapes

Thin-skin eddy-current inversion for the determination of crack shapes

Space mapping methodology for defect recognition in eddy current testing – type NDT

Temperature Independent Defect Monitoring Using Passive Wireless RFID Sensing System

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