Interferometric Technique for the Thermal Expansion Behavior of Carbon Nanocomposites

Carbon nanotube and nanoparticle-based materials and their composites are as yet small in scale and availability-consequently materials for the testing of properties are both scarce and of limited size. An optical technique based on Michelson interferometry has been developed to examine the through-thickness thermal expansion behavior of carbon multiwalled nanotube reinforced and un-reinforced woven silicon carbide/epoxy composites. The optical techniques took into account edge and end effects, in-plane curvature, compressive loading and optics positioning. The composite panels (7 x 10 mm) were approximately 0.66 mm thick. The through-thickness microstrain versus temperature was measured over the range 0-160 deg C and showed low coefficient of thermal expansion (CTE) values up to about 80 deg C with an increased CTE above the temperature corresponding to the expected glass transition of the matrix. The nanotubes had significant effects at lower temperatures, giving rise to a relatively large negative CTE. This was semi-quantitatively verified by additional quartz dilatometer measurements. The results are explained by the microstructure and prior knowledge that carbon nanotubes have negative volumetric CTE values at lower temperatures.