Porosity and Inclusion Detection in CFRP by Infrared Thermography

The ever wide use of composite materials in the aeronautical industry has evidenced the need for development of ever more effective nondestructive evaluation methodologies in order to reduce rejected parts and to optimize production costs. Infrared thermography has been recently enclosed amongst the standardized non destructive testing techniques, but its usefulness needs still complete assessment since it can be employed in several different arrangements and for many purposes. In this work, the possibility to detect slag inclusions and porosity is analyzed with both lock-in themography and pulse thermography in the transmission mode. To this end, carbon-fiber-peinforced polymers different specimens are specifically fabricated of several different stacking sequences and with embedded slag inclusions and porosity percentages. As main results, both of the techniques are found definitely able to reveal the presence of the defects above mentioned. Moreover, these techniques could be considered complementary in order to better characterize the nature of the detected defects. 1. Introduction In the last thirty years a huge employment of carbon-fiber-reinforced polymers (CFRPs) has characterized the production of components in the aerospace industry [1]. Indeed, since their introduction in the civil aviation in the eighties, CFRPs have gained a progressive interest due to their versatility (e.g., perfectly matching the design requirements) as well appreciable low weight and high stiffness with costs saving. However, due to the many parameters involved in the CFRP manufacturing process, special care must be devoted to production control [2], in order to reduce rejected parts, and to detect, at the onset stage, buried defects, which may, unpredictably, grow once the structure is under load. Moreover, the intrinsic nonhomogeneities of the components and their properties, which are strictly dependent on the fiber quantity and orientation, make them susceptible to damage if impacted, also at low energy. This is why strong efforts have been paid by the industries to develop ever more effective non destructive testing and evaluation techniques [3]. Great attention was devoted, in the last twenty years, to the use of infrared thermography, (IRT) for non destructive evaluation (NDE) of materials and, recently, it was included amongst the standardized NDE techniques in the aeronautical field [4]. The main advantages of IRT are related to its contactless character and fast rate of inspection of large components. It can be used as complement to, or substitute, of the most