Characterisation of adhesively bonded laminates using radiography and infrared thermal imaging techniques

This paper discusses the studies undertaken to establish the limits of detectability of glue variations and defect detection in adhesively bonded canopy specimens used in fighter aircrafts, by low-energy radiography and thermal imaging techniques. The complementary nature of radiography and thermal imaging is also highlighted. From the results of the experiments, it is shown that low-energy radiography reveals volumetric defects such as porosities as small as 170 microns; thermal imaging is more sensitive to evaluate variations in glue content, having the capability of detection of variations in glue content of the order of 20%. Thermal imaging did not indicate the Presence of any major defects such as delaminations and debonds. While reflection and through-transmission-based thermal imaging techniques can be utilised for the detection of glue variations, the rate of change of temperature by transmission technique being higher, this can serve as a more sensitive indicator of glue variations, if both sides access is feasible.