Smart methods for assessing the integrity of a composite structure are essential to both reduce manufacturing costs and
out of service time of the structure due to maintenance. Nowadays, thermal non-destructive testing (NDT) is commonly
used for assessing composites. This research work evaluates the potential of various infrared thermography (IRT)
approaches for assessing different types of fabricated defects (i.e. impact damage, inclusions for delaminations, etc) on
Glass Fibre Reinforced Polymer (GFRP) and Carbon Fibre Reinforced Polymer (CFRP) plates. Measurements were
performed using LWIR and three active approaches: a) pulsed thermography using the flash method (xenon flash
lamps), b) transient themography using IR-heating pulse, and c) thermographic inspection for cooled sample by freezing
in -20 °C and then use monitoring. Furthermore, integrated flash thermography by employing a MWIR system was also
Penetrated water in the composite sandwich structures has caused problems in aircraft structures. Flight surfaces have
been lost during the flights, because moisture corrodes the honeycomb and further reduces the strength of the adhesive.
Water can also cause additional defects during the composite repairs, which have resulted because of the expansion of
the moisture (in closed cavity), hence causing skin blow core phenomena during the curing cycle (heating) of the repair.
Thermographic investigation is done to find a suitable procedure to find penetrated water from the composite aircraft
structures by cooling the whole structure, or separated parts of the aircraft, under freezing conditions. Thermographic
inspection based on the phase transition of water exploits the phase transition energy that is needed for the water
defrosting (melting). Advantage of this method is that no additional excitation source is needed for the tests. Method
based on phase transition can be especially exploited during the long period of arctic weather conditions in Finland and
other cold areas. Aircraft can be either inspected right after a flight, or it can be left outside in freezing conditions
overnight and inspected when it has been brought in to the maintenance hall to warm conditions.