Investigation of effect of CNT weight fraction on smart paint for structural health monitoring of carbon fiber reinforced composites

The increased use of composites for load-carrying structures, bring out the critical problem that strain and damage sensing to maintain reliable structures. In this study, carbon nanotube (CNTs) polymer nanocomposites (CNT-PNCs) as a smart paint were used as a strain sensor to follow the mechanical deformations of the structures. First, CNT polymer nanocomposites (CNT-PNCs), with three different CNT weight fractions (0.1, 0.25 and 0.5), were prepared by adding CNTs into the epoxy by shear mixing. Effect of CNT weight fraction on electrical conductivity of CNT-PNCs were investigated by 2-probe electrical conductivity measurement. The results show that even at low concentrations of CNT the electrical conductivity is beyond the percolation threshold. Within these results CNT-PNCs were applied on to the surface of composite structures as a smart paint for in-situ Structural Health Monitoring (SHM). Cyclic loading were applied onto the specimens at a constant voltage of 10 V and the stress and resistivity change data were obtained simultaneously. The test results showed a proper compliance with a damage of the composite structure.