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Comparison of lock-in and pulse compression thermal imaging techniques for non-destructive defect detection
D. Roy,
Published in British Institute of Non-Destructive Testing
In recent years, thermal imaging has played an increasingly important role in the area of nondestructive testing for subsurface defects. The two predominantly used thermal imaging techniques arelock- in thermography and pulse thermography. Lock-in thermography is based on periodically heating a test-piece. The resultant periodic temperature variation resembles a wave and is known as a thermal wave. It's propagation is characterised by changes in phase and amplitude and this information generates the phase and amplitude thermal images. Pulse compression thermal imaging is a relatively new defect detection technique. Herein a thermal excitation within a band of frequencies is incident on the sample and processed with a reference signal to generate an output identical to that of a pulsed thermography experiments. A comparison between the two techniques for defect detectability is presented on a Carbon-Fibre Reinforced Polymer (CFRP) sample with machine blunt holes of varying depths. The experiments are conducted at different frequency range necessary to produce thermal diffusion lengths to cover the set of defect depths to be detected.
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Published in British Institute of Non-Destructive Testing
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