Abstract
In situ sensing of damage in epoxy embedded separately with carbon nanotubes (CNTs) and carbon black (CB) microparticles is investigated under quasi-static uniaxial tensile loading. Three different weight fractions of CNTs (0.1, 0.3%, and 0.5%) and one-weight fraction of CB (10%) are used to generate a conductive network in epoxy. A modified four circumferential ring probes technique is employed and a constant current was applied through the outer probes. The resulting voltage drop between the inner probes is measured using a high-resolution electrometer-based system to determine the resistance change associated with nonlinear deformation, damage initiation, and growth in the material. As the generated conductive network is different with changing weight fractions of CNTs, the resulting electrical response was identified to be significantly different between composites. The nonlinear deformation associated with the unfolding of entangled polymer chains and further straightening of them, decreased the distance between neighboring CNTs, resulting in improved electron hopping. For CB-embedded epoxy, a very high percentage increase in resistance is noticed when compared to CNTs case owing to induced microcracks associated with agglomerated CB particles. POLYM. COMPOS., 2012. (c) 2012 Society of Plastics Engineers