Ultrasensitive embedded sensor for composite joints based on a highly aligned carbon nanotube web

Herein, we present a novel approach for damage sensing in adhesively bonded joints using a carbon nanotube single layer web (CNT-SLW) which marks a significant departure from the approach of dispersing CNTs within epoxy resins. In this work, a very thin, highly aligned CNT-SLW (densified thickness ∼ 50 nm) with aerial density of 2.0 μg/cm2 was horizontally drawn from a vertically aligned CNT forest, positioned over an adhesive film, which was, in turn, placed between two non-conductive composite adherents. This was followed by the application of heat and pressure to cure the adhesive. These joints were subjected to quasi-static and cyclic loading to investigate the damage sensing performance of a CNT-SLW. The CNT-SLW sensor, placed parallel to the load direction, exhibits remarkably high cyclic stability as well as exceptionally high sensitivity to damage initiation and accumulation. The resistance increase (ΔR/Ro% ∼1633%) is significantly higher than that of adhesive sensors with dispersed CNTs/graphene reported in the literature. Morphological studies help to explain the sensing mechanism through interactions of the CNT-SLW with the evolution of micro-cracks. These results demonstrate the potential of macroscopic architectures of CNTs, with controlled orientation, for the development of high performance structural health monitoring (SHM) systems for damage detection.