November 15, 2018 – Carbon fiber composites—lightweight and strong—are great structural materials for automobiles, aircraft and other transportation vehicles. They consist of a polymer matrix, such as epoxy, into which reinforcing carbon fibers have been embedded. Because of differences in the mechanical properties of these two materials, the fibers can detach from the matrix under excessive stresses or fatigue. That means damage in carbon fiber composite structures can remain hidden below the surface, undetectable by visual inspection, potentially leading to catastrophic failure.
“Carbon fiber composites fail catastrophically, so you won’t see damage until the entire structure has failed,” said Chris Bowland, a Wigner Fellow at the Department of Energy’s Oak Ridge National Laboratory. “By knowing what’s going on within the composite, you can better judge its health and know if there is damage that needs to be repaired.”
Recently, Bowland and Amit Naskar, leader of ORNL’s Carbon and Composites Group, invented a roll-to-roll process to coat electrically conductive carbon fibers with semiconducting silicon carbide nanoparticles. This nanomaterial-embedded composite is stronger than other fiber-reinforced composites and imbued with a new capability—the ability to monitor its own structural health.
When enough coated fiber is embedded in a polymer, the fibers create an electrical network and the bulk composite becomes electrically conductive. The semiconducting nanoparticles can disrupt this electrical conductivity in response to applied forces, adding an electromechanical functionality to the composite.
If the composite is strained, the connectivity of the coated fibers is disrupted and the electrical resistance in the material changes. Should storm turbulence cause a composite airplane wing to flex, an electrical signal may warn the plane’s computer that the wing has endured excessive stress and prompt a recommendation for an inspection.
ORNL’s roll-to-roll demonstration proved in principle that the method could be scaled up for high-volume production of coated fibers for next-generation composites. Self-sensing composites, perhaps made with a renewable polymer matrix and low-cost carbon fibers, could find themselves in ubiquitous products, even including 3D-printed vehicles and buildings.
To fabricate nanoparticle-embedded fibers, the researchers loaded spools of high-performance carbon fiber onto rollers that dipped the fiber in epoxy loaded with commercially available nanoparticles about the width of a virus (45–65 nanometers). The fiber was then dried in an oven to set its coating. Read more