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The effects of inner microstructures, including crystallite size, orientation and defects on the stiffening phenomena of PAN-based T300 carbon fibers under tension were explored. Single-fiber tensile test was conducted on three types of fiber: as received, 1400 and 1600 °C heat treated. The distribution of crystallite orientation in a fiber from core to skin was obtained by using transmission electron microscopy. The observations indicate the load-transfer between crystallites depends on the crystallite entanglement. The slide-lock of the entangled junctions among the loosely compacted crystallites is responsible for the increasing elastic modulus during tension. The sharp drop of tensile strength (−36%) of the fiber after heat treated at 1600 °C was attributed to the increasing of crystallite size, nano-pore defects and a higher misalignment of crystallites in the core region.

Reduced graphene oxide paper was fabricated by incorporating dopamine. By using adhesive property, reducing ability, high thermal stability, and high carbon-yielding characteristic of dopamine, the dopamine-embedded graphene oxide paper can be mechanically stronger, thermally more stable, and electrically more conductive compared to conventional graphene oxide paper. Herein, in order to preserve a planar structure of graphene sheets and obtain free-standing paper, a simple one-step fabrication method was introduced, in which vacuum-assisted filtration of a graphene oxide suspension and polymerization of dopamine proceed at the same time. The manufactured paper had sequentially layer-stacked and planar structure of graphene sheets and polydopamine. The paper showed increased tensile strength and elongation, and higher thermal stability. Electrical conductivity was recovered, which was not measurable in conventional graphene oxide paper. To investigate enhancement of reduction, thermal annealing was further carried out. As a result, a critical reduction temperature was lowered and higher electrical conductivity was recorded at all annealing temperatures.

Vapor grown carbon nanofibers (VGCNFs) were deposited on carbon fibers (CFs) using electrophoretic deposition (EPD). Composites of the resulting hybrid material (CF-VGCNF) in an epoxy matrix were fabricated by the vacuum-assisted resin transfer molding process. The electrical conductivities of the composites were significantly improved compared to those without the VGCNF reinforcement. The Taguchi method was used to optimize the EPD process conditions through the analysis of means and the analysis of variance for achieving a highly uniform deposition of carbon nanofibers. The parameters considered for optimization are: deposition time, applied voltage, concentration of VGCNF in a distilled water suspension, and the distance between anode (a carbon fabric) and cathode (a copper plate). An orthogonal array of L 9 (3 4 ) was created in the statistical design of experiments. The through-thickness electrical conductivity of the composites produced using the optimum deposition conditions was more than 90 times that of carbon fiber/epoxy composites. When compared with the average electrical conductivity of the nine design experiments, the electrical conductivity of the CF-VGCNF/epoxy composite using a filler prepared under the optimum deposition conditions showed a 51% improvement.

Continuous fibers composed of carbon nanotubes have been adopted as reinforcements for polymeric composites. This paper presents several fundamental studies relevant to the mechanical behavior of CNT fibers, including fiber tensile behavior; in situ SEM observation of fiber deformation mechanisms; and fiber modulus, ultimate strength and fracture strain measurements. A modified Weibull strength distribution model that takes into account the flaw density variation with fiber diameter has been adopted for the statistical strength analysis. The interfacial shear strength between the carbon nanotube fiber and the epoxy matrix has been measured using fragmentation tests of single-fiber composites.