Spatial damage detection in electrically anisotropic fiber-reinforced composites using carbon nanotube networks

Due to their small size, carbon nanotubes are able to create electrically conductive networks surrounding structural fiber reinforcements in composites. As damage accumulates in the polymer matrix, cracks break the nerve-like conducting pathways resulting in bulk changes in electrical resistance. To utilize carbon nanotube networks as a potential structural health monitoring (SHM) approach it is necessary to develop techniques capable of detecting localized and site-specific damage. Electrically anisotropic composites were manufactured from unidirectional glass fibers treated with a sizing containing carbon nanotubes. Local damage was introduced to the composite laminates and was assessed by taking electrical measurements from an array of surface mounted electrodes. Conductivity maps generated using electrical impedance tomography (EIT) were compared to the normalized resistance change approach. A center of mass approach was utilized to define the damage location. Both techniques are capable of localizing damage in the composite but EIT has much higher overall spatial sensitivity. The normalized resistance change approach, however, requires significantly fewer measurements and can be utilized for real-time detection of damage.