Thring, C.B. , Fan, Y. and Edwards, R.S. (2016) Focused Rayleigh wave EMAT for characterisation of surface-breaking defects. NDT and E International, 81, pp. 20-27. (doi: 10.1016/j.ndteint.2016.03.002)
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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 modelling, 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 plus or minus 0.5 mm. The results can be used to design an EMAT with optimised focal behaviour for defect detection.
| Item Type: | Articles |
|---|---|
| Keywords: | Ultrasonics, EMAT, focusing, Rayleigh wave. |
| Status: | Published |
| Refereed: | Yes |
| Glasgow Author(s) Enlighten ID: | Thring, Dr Claire |
| Authors: | Thring, C.B., Fan, Y., and Edwards, R.S. |
| College/School: | College of Science and Engineering > School of Engineering > Systems Power and Energy |
| Journal Name: | NDT and E International |
| Journal Abbr.: | NDT&E International |
| Publisher: | Elsevier |
| ISSN: | 0963-8695 |
| ISSN (Online): | 1879-1174 |
| Published Online: | 12 March 2016 |
| Copyright Holders: | Copyright © 2016 Elsevier Ltd. |
| First Published: | First published in NDT & E International 81: 20-27 |
| Publisher Policy: | Reproduced in accordance with the publisher copyright policy |
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