Detection and localization of impact damages in carbon nanotube–modified epoxy adhesive films with printed circuits

The study deals with an online monitoring approach for adhesively bonded composite joints. A modification of epoxy-based adhesive films with carbon nanotubes allows for electrical resistance measurements through the bonding via inkjet-printed silver conductive circuits on the composites structure. Impact damages are introduced into adhesively bonded glass fiber–reinforced polymer specimens. In-plane and through-thickness electrical resistance measurements show the possibility of accurate damage detection and damage localization of the introduced damages in one or two dimensions, depending on the conductive path designs. The measured electrical resistance changes are compared with results from ultrasonic inspections and light microscopy observations. Furthermore, a linear correlation of electrical resistance and bond line thickness was found. The results demonstrate the applicability of the presented method in a structural health monitoring system.