In a series of experiments, panels were made, variously, from layers of as-spun PAN nanofibers, layers of stabilized PAN nanofibers, or layers of carbonized nanofibers inserted between plies of aerospace- grade composites consisting of epoxy matrices reinforced with conventional carbon microfibers. Panels were also made without nanofibers between the plies. The panels were subjected to fracture-mechanics and edge delamination tests. The results of the fracturetoughness tests showed that the nanofibers at the different stages of manufacture afforded different degrees of toughening. The greatest toughening was found to occur in the panels containing carbonized nanofibers. The results of the edge delamination tests (for example, see figure) were interpreted as signifying that reinforcement by continuous carbon nanofibers yielded increases in delamination onset stress, ultimate strength, and fatigue life.

In other experiments, to demonstrate feasibility of manufacture, composite panels were made from sheets of continuous carbon nanofibers (without conventional carbon microfibers) stacked and impregnated with epoxy and cured at controlled temperature and pressure. Tests of the panels revealed substantial anisotropy of mechanical properties.

Continuous carbon nanofibers can be produced at a cost regarded in the art as reasonable in comparison with the costs of producing such other high-performance materials as carbon nanotubes. The continuity of these fibers reduces (relative to carbon nanotubes) the costs of handling and processing into nanocomposites. Newly developed methods of aligning nanofibers enable the fabrication of nanofiber products having superior anisotropic properties. In addition, these methods enable the fabrication of nanocomposites containing higher volume fractions of fibers and complex nanoreinforcement architectures.

This work was done by Y. A. Dzenis of the University of Nebraska for the Air Force Research Laboratory.

AFRL-0039

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