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Focused Rayleigh wave EMAT for characterisation of surface-breaking defects
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Thring, C. B., Fan, Yichao and Edwards, R. S. (Rachel S.) (2016) Focused Rayleigh wave EMAT for characterisation of surface-breaking defects. NDT & E International, 81 . pp. 20-27. doi:10.1016/j.ndteint.2016.03.002
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Official URL: http://dx.doi.org/10.1016/j.ndteint.2016.03.002
Abstract
Developments towards higher resolution and the ability to detect small defects are bringing a step-change in non-destructive testing. This paper presents a new method for increasing resolution, using a focused electromagnetic acoustic transducer (EMAT) optimised to generate Rayleigh waves at 2 MHz. This high frequency allows detection of mm-depth defects, and the focusing allows sizing of much shorter defects than is possible when using standard EMATs. The focusing behaviour and the aperture angle effect are analysed using laser vibrometry and finite element modeling, showing that a reduced aperture shifts the focal point from the designed value and increases the focal depth. The dual-EMAT has excellent signal to noise ratio (up to 30 dB) and has been used in single shot mode to image a variety of surface-breaking defects, including detecting and positioning a pair of real defects in an aluminium billet sample, and a machined defect of 2 mm length, 0.2 mm width, and 1.5 mm depth, giving an upper limit on the defect length of 2.1 +- 0.5 mm. The results can be used to design an EMAT with optimised focal behaviour for defect detection.
| Item Type: | Journal Article | ||||||||||
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| Subjects: | Q Science > QC Physics T Technology > TA Engineering (General). Civil engineering (General) |
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| Divisions: | Faculty of Science > Physics | ||||||||||
| Library of Congress Subject Headings (LCSH): | Ultrasonics, Rayleigh waves | ||||||||||
| Journal or Publication Title: | NDT & E International | ||||||||||
| Publisher: | Elsevier Sci Ltd. | ||||||||||
| ISSN: | 0963-8695 | ||||||||||
| Official Date: | July 2016 | ||||||||||
| Dates: |
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| Volume: | 81 | ||||||||||
| Number of Pages: | 8 | ||||||||||
| Page Range: | pp. 20-27 | ||||||||||
| DOI: | 10.1016/j.ndteint.2016.03.002 | ||||||||||
| Status: | Peer Reviewed | ||||||||||
| Publication Status: | Published | ||||||||||
| Access rights to Published version: | Restricted or Subscription Access | ||||||||||
| Funder: | Engineering and Physical Sciences Research Council (EPSRC), University of Warwick |
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