Near Field Enhancements from Angled Surface Defects; A Comparison of Scanning Laser Source and Scanning Laser Detection Techniques
- 172 Downloads
Enhancement of the Rayleigh wave signal amplitude at a surface defect, due to interference of incident, reflected and mode converted waves, has been reported by several authors, and it has been suggested that this could be used as a fingerprint of the presence of such cracking. The scanning laser line source technique in particular, where signal amplitude is enhanced as the laser generating the Rayleigh waves is in the region of a surface defect, has been reported as a suitable detection tool. However, the previous work has looked primarily at defects propagating normal to the surface, which may not always be a suitable approximation, and the enhancement measured when a detection laser rather than a generation laser is near a crack may, in some cases, be more significant. This work explores near field effects for both laser generation and laser detection points near a defect, and compares the enhancements for defects which are angled relative to the surface. We use a combination of finite element method models and experimental results, and probe enhancements of both the amplitude and frequency signals, and show that scanning the detection point may be a better method for locating surface defects if they are inclined at an angle to the surface.
KeywordsRayleigh wave Enhancement Surface defect NDT Ultrasound
Unable to display preview. Download preview PDF.
- 2.Kromine, A.K., Fomitchov, P.A., Krishnaswamy, S., Achenbach, J.D.: Laser ultrasonic detection of surface breaking discontinuities: Scanning laser source technique. Mater. Eval. 58(2), 173 (2000) Google Scholar
- 4.Edwards, R.S., Jian, X., Fan, Y., Dixon, S.: Rail defect detection using ultrasonic surface waves. In: Review of Progress in Quantitative Nondestructive Evaluation, vols. 25A/B. AIP Conference Proceedings, vol. 820, pp. 1601–1608 (2005) Google Scholar
- 13.Scruby, C.B., Drain, L.E.: Laser Ultrasonics: Techniques and Applications. Adam Hilger, Bristol (1990) Google Scholar
- 17.Fujii, K.: Rayleigh-wave scattering at various wedge corners—investigation in the wider range of wedge angles. Bull. Seismol. Soc. Am. 84(6), 1916 (1994) Google Scholar
- 18.Dutton, B., Rosli, M.H., Edwards, R.S.: Defect feature extraction using surface wave interactions and time-frequency behaviour. In: Review of Progress in Quantitative Nondestructive Evaluation, vols. 29A/B. AIP Conference Proceedings, vol. 1211, pp. 647–654 (2010) Google Scholar
- 19.Dutton, B., Clough, A.R., Rosli, M.H., Edwards, R.S.: Exploring surface wave interaction with angled defects in the near and far field. J. Phys. Conf. Ser., 2nd International Symposium of Laser-Ultrasonics, in press Google Scholar
- 20.Dutton, B., Clough, A.R., Rosli, M.H., Edwards, R.S.: Non-contact ultrasonic detection of angled surface defects. NDT E Int., in press Google Scholar
- 21.Essex, S.D., Potter, M.D.G., Vann, R., Dixon, S.: Utilizing EBSD to validate and understand NDE techniques. In: Review of Progress in Quantitative Nondestructive Evaluation, vols. 28A/B. AIP Conference Proceedings, vol. 1096, pp. 1224–1231 (2009) Google Scholar
- 22.PZFlex version 2.3, developed by Weidlinger Associates, Inc., http://www.pzflex.com/
- 27.Viktorov, I.A.: Rayleigh and Lamb Waves: Physical Theory and Applications. Ultrasonic Technology. Plenum Press, New York (1967) Google Scholar
- 28.Dutton, B., Clough, A.R., Edwards, R.S.: Ultrasound near field enhancement mechanism for angled surface defects. In preparation Google Scholar