Carbon composite strengthening: Effects of strain rate sensitivity and feature size

Strain rate sensitivity of strength is analyzed for a bulk, turbostratic carbon reinforced epoxy resin composite. The strength of the composite was measured using a rate-modified version of the standard, 3-point bending test. Rate sensitivity of stress was calculated by varying the strain rate of stress on the samples, and measuring the increase in yield strength. Metal reinforced carbon matrix composite coatings were also examined, with CuC, NiC, and CuNiC samples analyzed using nano-indentation and tapping mode AFM hardness and modulus measurements. The carbon structures within the coatings are nanoscale, and characterization of the carbon features in the coatings and the bulk fiber composite allow for conclusions to be drawn regarding the structured relationship within metallic and non-metallic carbon composites. For the fibers, we find that bending strength is rate sensitive as attributed to the turbostratic carbon-fiber component. The material has a strength to weight ratio comparable to Ti-6Al-4V alloy. For the coatings, we find that the hardness and elastic modulus are dependent on whether the morphology is layered versus particulate, with the nanodisperse morphology having the highest hardness and elastic modulus.