Principal Investigator Brian Wardle
Materials comprising carbon nanotubes (CNTs), such as hierarchical nanoengineered advanced compos- ites for aerospace applications, are promising new materials thanks to their mechanical and multifunc- well as overall morphology. Extensive mechanical and maltifunctional properties. We have undertaken a significant experimentally based program to understand both microstructures of aligned-CNT nanocomposites and hierarchical nanoengineered advanced composites macrostructures hybridized with aligned CNTs.
Aligned nanocomposites are fabricated by mechanical densification and polymer wetting of aligned CNT forests. Here the polymer is typically an unmodified aerospace-grade epoxy. CNT forests are grown to mm-heights on 1-cm2 Si substrates using a modified chemical vapor deposition process. Following growth, the forests are released from the substrate and can be handled and infiltrated. The volume fraction of the as-grown CNT forests is about 1%; however, the distance between the CNTs (and thus the volume fraction of the forest) can be varied by applying a compressive force along the two axes of the plane of the forest to give volume fractions of CNTs exceeding 20%. Variable-volume fraction-aligned CNT nanocomposites were characterized using optical, scanning electron (SEM), transmissiong electron (TEM) microscopy, 3-DTEM and X-ray computed tomography (CT) to analyze dispersion and alignment of CNTs as well as overall morphology. Extensive mechanical property testing and modeling are underway, including 3-D constitutive relations and fracture toughness.
Nanoengineered hierarchical composites hybridized with aligned CNTs are prepared by placing long (>20 μm) aligned CNTs at the interface of advanced composite plies as reinforcement in the through-thickness axis of the laminate (see Figure 2). Three fabrication routes were developed: transplantation of CNT forests onto pre-impregnated plies (“nanostitching”), placement of detached CNT forests between two fabrics followed by subsequent infusion of matrix, and in-situ growth of aligned CNTs onto the surface of ceramic fibers followed by infusion or hand- layup. Aligned CNTs are observed at the composite ply interfaces and give rise to significant improvement in interlaminar strength, toughness, and electrical properties. Extensions of the CNT-based architectures to ceramic-matrix nanocomposites and towards multifunctional capabilities are being developed, including structural health monitoring and deicing.