Porosity Distribution in Composite Structures with Infrared Thermography

Composite structures are increasingly used in the transport industry especially in the aeronautical sector thanks to their favorable strength-to-weight ratio with respect to metals. However, this is true if the final part is defects free and complies with quality requirements. A main weakness in composites is porosity, which is likely to be introduced during manufacturing processes and which may knock down the material characteristics affecting its performance in service. Porosity plays a key role in sandwich structures, which involve novel metal foams as core, since the foam performance strongly depends on size and distribution of pores. The determination of porosity is mostly attained by destructive methods, which supply only a general indication linked to the production part number. Conversely, composites may entail local significant variation of porosity, which may be discovered only with effective nondestructive techniques. The attention of the present work is focused on the possibility to use infrared thermography to get information about the amount and distribution of porosity. In particular, two techniques: flash thermography and lock-in thermography are used to comply with requirements of both monolithic composites and metal foams.