Thermal NDT of glass reinforced composite panels for naval applications by means of a linear infrared scanner

The work describes the development and application of a low cost Thermal NDT set-up to investigate the influence of delamination defects on thick glass fibre reinforced composite laminates simulating typical hull monolithic GRP panels. Two active thermographic techniques have been implemented in particular: a pulsed thermography and a step heating scheme. A 12 mm thick cross-ply panel has been manufactured and delamination defects simulated in two different ways: by embedding patches of folded Teflon sheets, and by drilling flat bottomed back holes. A number of defects was then positioned at three different depths form the scanned surfaces, measuring ¼, ½ and ¾ of the laminate thickness. A reflection set-up was adopted, with an external heat source consisting of 1500 W halogen lamps. Results have evidenced the possibility to use the proposed cheap thermographic set-up, suitable to operate also in boatyard environments, to detected non-visible delamination type defects in thick GRP laminate skins. A fine tuning of the operational parameters is though essential in order to better identify defects features and to discern the influence of other factors such as surface finish.