The next generation of composite materials can monitor their structural health.
Carbon fiber composites are lightweight and sturdy and are important structural materials for automobiles, aircraft and other vehicles. They consist of a polymer matrix, such as an epoxy resin, in which reinforced carbon fibers are embedded.
Due to the difference in mechanical properties of the two materials, the fibers will fall off the substrate under excessive stress or fatigue.
This means that damage to the carbon fiber composite structure may still be hidden below the surface and cannot be detected by the naked eye, which may lead to catastrophic failure.

Chris Bowland, a researcher at the US Department of Energy’s Oak Ridge National Laboratory, said: “By understanding the inside of the composite, you can better judge its health. And know if there is any damage that needs to be repaired.”
Recently, Bowland and ORNL’s carbon and composites team leader Amit Naskar invented a rolling strip method that encases conductive carbon fibers on semiconductor silicon carbide nanoparticles.

This nanomaterial-embedded composite is stronger than other fiber-reinforced composites and has a new ability to monitor the health of its structure.
When enough of the coated fibers are embedded in the polymer, the fibers form a power grid and the bulk composite conducts electricity.
Semiconductor nanoparticles can destroy this conductivity under the action of external forces, adding electromechanical functions to the composite.
If the composite is stretched, the connectivity of the coated fibers is destroyed and the electrical resistance in the material changes.
If storm turbulence causes the composite wing to bend, an electrical signal may warn the aircraft’s computer to alert the wing to excessive pressure and suggest a check.
ORNL’s rolling strip demonstration demonstrates in principle that the method can produce next-generation composite coated fibers on a large scale.

Self-sensing composites, perhaps made from renewable polymer matrices and low-cost carbon fibers, can find their place in ubiquitous products, even 3D printed cars and buildings.

By Claudine GUO