Nanotechnology may help aircraft manufacturers produce airframes that are lighter and stronger than ever. Researchers at the Massachusetts Institute of Technology (MIT, Cambridge, MA) are reinforcing the plies used in advanced composites by stitching them with nanotubes.

Using computer models of how such a material would fracture, “we convinced ourselves that reinforcing with nanotubes should work far better than all other approaches,” says Brian Wardle, an assistant professor in the Department of Aeronautics and Astronautics. He and his colleagues developed techniques for creating the nanotubes and for incorporating them into existing aerospace composites.

The polymer glue between two carbon-fiber layers is heated, becoming more liquid-like. Billions of nanotubes positioned perpendicular to each carbon-fiber layer are then sucked up into the glue on both sides of each layer. Because the nanotubes are 1,000 times smaller than the carbon fibers, they don’t detrimentally affect the much larger carbon fibers, but instead fill the spaces around them, stitching the layers together.

The advanced materials currently used for many aerospace applications are composed of layers of carbon fibers that are held together with a polymer glue. But, that glue can crack and cause the carbon-fiber plies to come apart.

Engineers have explored a variety of ways to reinforce the interface between the layers by stitching, braiding, weaving or pinning them together. However, all of those processes cause problems, because the relatively large stitches or pins penetrate and damage the carbon-fiber plies. “And, those fiber plies are what make composites so strong,” says Wardle.

Advanced composites reinforced with nanotubes are more than 1 million times more electrically conductive than their counterparts without nanotubes. As a result, aircraft built with such materials would have greater protection against lightning damage.

“We’re putting nanotubes in the place where the composite is weakest, and where they’re needed most,” explains Wardle. “Dramatic improvements can be achieved with nanotubes comprising less than 1 percent of the mass of the overall composite. In addition, the nanotubes should add only a small amount to the cost of the composite, while providing substantial improvements in bulk multifunctional properties.”