Exploring high-frequency eddy-current testing for sub-aperture defect characterisation using parametric-manifold mapping

Robert R Hughes*, Bruce W Drinkwater

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

Abstract

Accurate characterisation of small defects remains a challenge in non-destructive testing (NDT). In this paper, a principle-component parametric-manifold mapping approach is applied to single-frequency eddy-current defect characterisation problems for surface breaking defects in a planar half-space. A broad 1-8 MHz frequency-range FE-circuit model & calibration approach is developed & validated to simulate eddy-current scans of surface-breaking notch defects. This model is used to generate parametric defect databases for surface breaking defects in an aluminium planar half-space and defect characterisation of experimental measurements performed. Parametric-manifold mapping was conducted in N-dimensional principle component space, reducing the dimensionality of the characterisation problem. In a study characterising slot depth, the model & characterisation approach is shown to accurately invert the depth with comparable accuracy to an equivalent peak amplitude-phase inversion method. The approach is used to characterise the depth of a sloped slot demonstrating good accuracy up to ~2.0 mm$ in depth over a broad range of frequencies, indicating applications in geometric feature inversion. Finally the technique is applied to finite rectangular notch defects of surface extents smaller than the diameter of the inspection coil (sub-aperture) over a range of sub-resonant frequencies. The results highlight the limitations in characterising these defects and indicate how the inherent modelling uncertainty around resonance can severely limit characterisation at these frequencies.
Original languageEnglish
Article number102534
Number of pages11
JournalNDT and E International
Volume124
Early online date1 Sep 2021
DOIs
Publication statusPublished - 1 Dec 2021

Bibliographical note

Funding Information:
The authors would like to thank Dr Long Bai, Dr Alexander Velichko and Prof. John Bowler for their advise and insight, as well as James Wilcox from Rolls-Royce plc (NDT lab) for sizing and providing X-ray CT images of test specimen defects. This work was funded via the Research Centre for Non-destructive Evaluation (grant number EP/L022125/1). Data are available at the University of Bristol data repository, data.bris, at https://doi.org/10.5523/bris.335fggexk0y3a1zoxn6547htad.

Funding Information:
The authors would like to thank Dr Long Bai, Dr Alexander Velichko and Prof. John Bowler for their advise and insight, as well as James Wilcox from Rolls-Royce plc (NDT lab) for sizing and providing X-ray CT images of test specimen defects. This work was funded via the Research Centre for Non-destructive Evaluation (grant number EP/L022125/1 ). Data are available at the University of Bristol data repository, data.bris, at https://doi.org/10.5523/bris.335fggexk0y3a1zoxn6547htad .

Publisher Copyright:
© 2021 Elsevier Ltd

Structured keywords

  • Algorithms and Complexity

Keywords

  • NDT
  • NDE
  • Eddy-Current Testing
  • ECT
  • Defect characterisation
  • Modelling and Simulation

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