B S Wong, C G Tui, W Bai, P H Tan, B S Low and K S Tan
B S Wong and W Bai are at Nanyang Technological University
P H Tan was formerly at Nanyang Technological University
C G Tui and B S Low are at the Republic of Singapore Air Force
K S Tan is at the University of Brunei
This paper decribes experiments conducted with the lock-in thermographic procedure.
This technique monitors the thermographic interference pattern produced by an incident thermal wave with one returning from a subsurface defect. Hence, information is deduced concerning the defect. The information is derived from phase and amplitude plots from the interference pattern.
A fibre-reinforced composite specimen with defects of various sizes and depths below the test surface and also impact damaged honeycomb specimens were tested using lock-in thermography and ultrasonic C-scan. Thermography was found to be comparable to Cscan when testing for near surface defects and hence can be used in preference to Cscan. Also it has the advantages of on site testing, has increased speed and is a remote testing procedure.
The size and depth of small defects was found to significantly affect phase readings. A possible solution to this is to produce empirical software databases which could be used to evaluate defect depth from size and phase measurements
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http://www.ntu.edu.sg/mae/Research/programmes/Sensors/NDT/thermographybyBSWong.pdf