This paper focuses on the ability of carbon nanofibre (CNF) networks to in situ monitor fatigue induced disbond damage in adhesive bonded composite joints. The inclusion of CNFs in the epoxy adhesive increases its conductivity by five orders of magnitude. The improved electrical conductivity is utilized to evaluate the ability of the CNF network to monitor and detect the fatigue induced disbond damage by measuring the in-situ resistance changes using a four probe setup. The changes in total resistance was a function of the bulk electrical resistivity of the adhesive and the bond dimensions, which were related to the disbond length to model and determine the size of the disbond. The simple resistivity model was in good agreement with the resistance measured during fatigue testing. Good agreement was found between the optical disbond observations and the disbond length calculated using the proposed model. Finite element simulations were performed to ascertain the range of applicability of the proposed model. The simplicity of the disbond detection technique via direct current potential drop technique enables real time monitoring of crack growth in the composite structure
