Using infrared thermography to analyze substrate and adhesive effects in bonded structures

Abstract This study was focused on the application of infrared thermography for assessment of technological procedures used to improve adhesion in bonded structures. Infrared thermography is a remote imaging technique which can be fruitfully exploited either for mapping surface temperature in temperature-dependent manufacturing processes, or for nondestructive evaluation of end products. Basically, for nondestructive evaluation two different approaches are possible: traditional pulse thermography (PT) and lock-in thermography (LT) and the use of both techniques is discussed. Several specimens were fabricated to simulate different bonded structures that are used mainly in the aerospace industry. Such bonded structures included: adhesively-bonded aluminum joints with or without surface treatment before bonding, glass-reinforced epoxy composites and carbon-reinforced epoxy composites with or without plasma treatment before bonding. Pulse and lock-in thermographies are both capable of visualizing inhomogeneities in bulk materials, as well as disbonding, delamination, flaws and foreign inclusions in bonded structures. The results show that lock-in thermography is also capable of evaluating the effect of adhesive thickness and the effects induced in bonded structures by substrate surface treatments.