Repair integrity monitoring of composite aerostructures using thermographic imaging.

Bonded repair offers significant advantages over mechanically fastened repair schemes as it eliminates local stress concentrations and seals the interface between the mother structure and the patch. However, it is particularly difficult to assess the efficiency of the bonded repair as well as its performance during service loads. Thermography is a particularly attractive technique for the particular application as it is a non-contact, wide field non destructive method. Phase thermography is also offering the advantage of depth discrimination in layered structures such as in typical patch repairs particularly in the case where composites are used. Lock-in thermography offers the additional advantage of on line monitoring of the loaded structure and subsequently the real time evolution of any progressive debonding which may lead to critical failure of the patched repair. In this study composite systems (CFRP plates) with artificially introduced defects (PTFE) were manufactured. The aforementioned methods were employed in order to assess the efficiency of the thermographic technique. The obtained results were compared with typical C-scans.