Damage detection in honeycomb sandwich panels by active thermography

Infrared thermography is one of the effective non-destructive testing methods for damage characterization and identification in structural materials. Infrared thermography induces a temperature variation on the specimen and monitors the surface temperature to detect defects deep inside the structure. It offers advantages such as being non-contact inspect method, scanning large surface area and recording in real time. Although various techniques have been developed for infrared thermography, lock-in thermography (LT) and pulse thermography (PT) are the most preferred ones due to their rapid detection, in-service applicability. LT method uses a sinusoidal heat waves in different frequencies whereas PT, employs an instantaneous heat pulses to excite the specimen temperature and monitor its evolution to identify the defects and manufacturing flaws. In this study, both lock-in and pulse active thermography methods are used to detect different type of defects namely delamination, liquid ingress and debonding in a glass/phenolic prepreg with NomexTM honeycomb core sandwich composites which is a widely used material in aviation industry. The results are presented comparatively on the basis of advantages and disadvantages