Structural Health Monitoring of a CFRP Structural Bonded Repair by Using a Carbon Nanotube Modified Adhesive Film

Abstract Crack-sensing capabilities of a carbon nanotube (CNT) doped adhesive film have been analysed from coupon level to a composite repaired panel. Mechanical performance is not negatively affected by the addition of CNTs, due to their good distribution inside the adhesive. Moreover, the electrical resistance increases with displacement in both Single Lap Shear (SLS) and Mode-I joints, due to the combined effect of adhesive deformation and crack propagation . More specifically, Mode-I joints usually show a stick–slip behaviour with sharp increases and arrest phases in the electrical resistance, associated to changes in the failure modes. Furthermore, a structural health monitoring (SHM) test of a composite repair was carried out by different techniques such as acoustic emission , strain gauges and CNT adhesive monitoring. From electrical monitoring of the CNT adhesive, it is possible to identify some load thresholds from which the electrical resistance starts to increase. They coincide with sudden changes of the strain field monitored by the strain gauges, as well as, with sudden peaks of the sound level, being an indicative of crack nucleation, adhesive deformation and, finally, crack propagation. Therefore it highlights the great potential and robustness for on-line SHM purpose of the proposed CNT-doped adhesive films.