Out-of-autoclave fabrication and characterization of CNT-reinforced fiber reinforced plastics

The goal of this proposal is to advance knowledge on hierarchical integration of carbon nanotubes (CNTs) into carbon fiber reinforced plastics (CFRPs) using a low-cost and scalable out-ofautoclave (OOA) processing with magnetic field application, while achieving minimum voids and tailored CNT morphologies per desired property enhancement. Integration of lightweight CNTs into aerospace or other structural FRPs has been investigated for mechanical and multi-functional property enhancement, including interlaminar strength improvement. In addition to CNTs advanced properties, their agglomeration, morphologies, interfaces/interphases, and interactionswith fibers and matrices largely affect the resulting property improvement, even negatively for some cases. Maintenance of desired CNT dispersion and orientation during composite processing is a challenge. CNTs can be prepared as aligned, either as dry CNTs or as set in a B-staged polymer, but are prone to bend or buckle under the applied pressure (~100 psi) and the hydrodynamic forces during the curing process. In this work, the PIs aim to establish a new method to integrate CNTsinto CFRPs where the applied pressure is decreased to ~15 psi with the OOA processing and where magnetic fields keep CNT orientations and even drive them between fibers. First, nanoprepreg layers will be prepared by magnetically orienting CNTs within a B-staged thermoset polymer film and, second, the film will be partially integrated into a dry carbon fiber preform, forming a one-side-tacky (OST) prepreg. Finally, OST prepregs will be cured using vacuum-bag-only consolidation while magnetic fields are applied in the oven. Three technical objectives support the above goals. The first objective to understand the effectiveness of magnetic CNT alignment. Our previous study demonstrated successful alignment of nickel-doped multi-walled CNTs (~1 vol%), in moderately viscous matrices (up to ~100 cP) after short application (~30 mins) of a static magnetic field (400 G). Larger CNT volume fraction will improve interlaminar strengthening, but also will make magnetic alignment more challenging.The hydrodynamic force from consolidation will also make magnetic CNT alignment morechallenging, but, if properly controlled, can potentially help straighten CNTs. Such CNT assembly behaviors will be experimentally studied at relevant aero-gra the effects of Ni-doping and CNT alignment on mechanical properties, especially fracture toughness, of CNTepoxy composites. The fracture toughness of these CNT-epoxy composites will be characterized using 3-point bending and tensile tests, and will be correlated with CNT distributions. Subsequently, thin CNT nanoprepreg film (< 100 m) will be fabricated in a similar manner as theCNT-epoxy composites, and partially infused into a dry unidirectional carbon fiber preform. The third objective is to study the effect of the OOA consolidation process on CNT morphology change. Magnetic fields will be applied by permanent magnets during the OOA cure process to maintain the CNT alignment. The developed process aims to penetrate aligned CNTs into the fiber preform as the B-staged epoxy re-flows and impregnates the dry regions of the OST prepreg. The fabricated CNT-integrated FRPs will be characterized for their CNT distribution in the interlaminar regions and for their Mode I and II interlaminar fracture toughness. If successful, the proposed pro existing composites and metals. The emerging OOA process avoids the need for high cost equipment and tooling, thereby reducing the entry barrier for composites manufacturers. This abstract is approved for public release.