Crack imaging by scanning laser-line thermography and laser-spot thermography

T Li, Darryl P Almond, D Andrew S Rees

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The thermographic images of laser-heated spots or lines are perturbed by nearby cracks, providing NDE techniques for crack detection. Scanning with a laser line, rather than a laser spot, results in a substantial reduction in inspection time. 3D finite difference modelling results are presented that show the sensitivity of the laser-line thermography technique to cracks of varying lengths, depths and openings. A novel crack imaging technique is presented that is based on assembling the second spatial derivative thermal images of a scanned laser line. Experimental results show the new technique to image cracks with openings as small as a few micrometres. The scanning time of the laser-line thermography technique is shown to be over an order of magnitude smaller than that of the laser-spot thermography technique whilst producing crack images of similar quality.
Original languageEnglish
Article number035701
Number of pages14
JournalMeasurement Science and Technology
Issue number3
Early online date1 Feb 2011
Publication statusPublished - Mar 2011


  • cracks
  • nondestructive evaluation
  • laser
  • thermography


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