In-situ structural health monitoring of carbon fiber reinforced composites with CNT smart paint

Advanced composites, such as carbon fiber reinforced composites (CFRPs) with their heterogeneity and and anisotropy often shows failure beneath the surface of the structures. Traditional structural health monitoring (SHM) techniques applied to CFRPs has several constraints such as on ground measurements, cost, complex instrumentation within local areas and directions. In recent years a novel advancement about SHM applications is to use carbon nanotubes (CNTs) as strain or damage sensors by integrating them into composites or applying as coatings/paints on to the surface of structures are emerging and developing approaches. In this work, a preliminary study were presented about the results of using CNT smart paint as a strain sensor for detection through piezoresistivity. This invasive method allows to investigate CNT paint for SHM method to maintain safety in composites which also can act as protective environmental coating for CFRPs. The production of CNT smart paint is achieved through a two step dispersion of CNTs within epoxy by shear and mechanical mixing in several weight fractions (0.1, 0.25 and 0.5%) and then the paint was applied as a thin layer onto the CFRPs surface. To achieve in-situ SHM, a constant voltage of 10 V was applied to conductive paint while tensile forces were being applied to the test specimens. Strain and resistivity change data were obtained simultaneously and according to the test results, the test specimens coated with CNT smart paint showed an incremental trend for resistivity change vs. axial displacement.