Carbon nanotubes, atom-thick sheets of carbon, are among the strongest known materials. They already add their strength and toughness to several products on the market, including many bicycle frames. It's not surprising, then, that carbon nanotubes can also improve the properties of advanced aerospace materials.

Airplane skins are composed of composite materials made up of layers of carbon fibers held together by polymer glue. They can fail when the glue cracks and the fibers come apart, and reinforcing them is tricky. Using pins and stitching might seem like a good idea, but this can pierce and weaken the carbon layers. Researchers led by Brian Wardle, an assistant professor of aeronautics and astronautics at MIT, have now strengthened these advanced aerospace materials with what they call "nanostitching." Rows of carbon nanotubes perpendicular to the carbon microfibers fill the spaces between them, reinforcing the fiber layers without piercing them.

According to theoretical work to be published by the MIT group in the Journal of Composite Materials, these materials are not only 10 times stronger than those that don't contain nanotubes, but they are also more than one million times more electrically conductive, which suggests that they might protect aircraft from lightning strikes.

MIT aeronautics and astronautics professor Brian Wardle shows a composite material strengthened by carbon nanotubes. Credit: Donna Coveney/MIT