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. 1. Introduction Composite structures are increasingly used in the transport industry especially in the construction of aircraft [1] thanks to their favorable strength-to-weight ratio with respect to metals. Adversely, one of the main problems is related to their intrinsic inhomogeneous structure and to defects that can be inadvertently induced during their manufacture. The mostly used composites include a polymeric matrix reinforced with either carbon, or glass fibers, which are generally referred to as fiber reinforced polymers (FRPs). Generally, plies of fibers impregnated with resin are overlaid owing to a fixed stacking sequence and cured in autoclave. The autoclave cycle involves the combined effects of temperature and pressure. Temperature is needed to activate and to control the chemical reactions in the resin, while pressure may squeeze off the resin in excess to consolidate the stacked plies and to minimize the amount of entrapped gas between the plies and within the resin [2]. In particular, setting up the vacuum pressure and maintaining it for a fixed interval have been individuated as critical parameters to be carefully monitored [3, 4] to avoid undesired formation of voids in the laminate. In fact, the presence of porosity can reduce the interlaminar shear strength causing delamination (interlamina
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