No abstract

Several hybrid composite architectures with aligned carbon nanotubes have been shown to provide interlaminar reinforcement of fiber reinforced composites. Aligned carbon nanotubes (CNTs) grown on the surface of woven fibers is one such 'fuzzy fiber' reinforced plastics (FFRP) composite that provides mechanical reinforcement in the interlaminar and intralaminar regions, with large (> 1 kJ/m 2 ) increases in Mode I toughness observed previously. Here, the effects of cloth weave and CNT length on Mode I toughness is investigated as part of ongoing work to elucidate mechanisms contributing to interlaminar reinforcement in such hybrid systems. The system considered here differs from prior work in that an aerospace-grade resin is utilized and the composites are fabricated via infusion rather than hand lay-up. The Mode I response for two cloth weaves is studied, as well as a preliminary study on the effect of CNT length using one of the weaves. A moderate increase in steady-state Mode I toughness of ~20% is observed in the new laminate system for CNTs of ~20 µm in length, with a decrease in steady-state toughness noted for shorter (6 µm) CNTs in preliminary tests. The potential of these multi-scale interface hybrid composites for aerospace applications has yet to be fully harnessed without further investigation along the directions begun in this work. Nomenclature CNT= carbon nanotube CVD = catalyst vapor deposition DCB = double cantilever beam G Ic = Mode I interlaminar fracture toughness FFRP = fuzzy fiber reinforced plastic FRP = fiber reinforced plastic VARI = vacuum assisted resin infusion

The theoretical elastic properties of aligned carbon nanotube polymer nanocomposites (A-PNCs) have been predicted by standard composite theory, however, a complete experimental characterization of their (presumed) transversally isotropic properties has not been presented to date. High volume fraction A-PNCs are fabricated by biaxial mechanical densification of the CNTs, followed by polymer infiltration via capillarity-assisted wetting using an aerospace-grade epoxy. Because of the dimensions of the samples (~1mm 3 ), only bulk compression or nanomechanical tests have been attempted previously. Here, optical strain mapping is used in conjunction with simple mechanical loadings (here simple uniaxial dogbone specimens) in order to characterize the linear elastic constitutive relations of this material. Elastic stiffness is in agreement both with prior experimental nanoindentation measurements and finite element calculations that include the effects of waviness of the reinforcing CNT 'fibers'. NomenclatureA-PNC = aligned carbon nanotube polymer nanocomposite CNT = carbon nanotube CVD = chemical vapor deposition VACNT = vertically aligned carbon nanotube