This work analyses the capability of the application of self-sensing film adhesives for assessing the structural integrity of typical aeronautical bonded joints without altering its mechanical behavior. Tests have been carried out on carbon fiber reinforced polymer composites (CFRP) although the method has been also validated on aluminum substrates, showing that different types of strain and damage are detected depending on the characteristics of the joined materials. In both cases, the structural health monitoring of the bonded joints has been achieved. The developed technologies are based on the addition of carbon nanotubes (CNT) to the film adhesives in order to provide electrical conductivity to the different interfaces. The high conductivity and relative large aspect ratio of CNT result in percolation thresholds around 0.1% weight of carbon nanotubes in the adhesive. The CNT network formed in the adhesive offers significant potential to develop sensing for damage detection and health monitoring using direct-current measurements. Loads applied over the nanodoped adhesives produce damage (i.e. cracks, delaminations,...) appearance and/or damage progression in the material, that modifies the integrity of carbon networks and increases the electrical resistivity of the adhesive. Two different methods have been developed to deposit CNTs on film adhesives: innovative inkjet printing methods and mask methods. In both cases the CNTs used were stabilized in water solution to use a solvent that did not damage the behavior of the adhesive. Then, the CNT solution was incorporated in the nanoreinforcement with controlled geometries over the films, providing local and controlled sensitivity to the bonded joints and giving information of the location of the damages, their characteristics and their propagations in an accurate way.
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