MIT Engineers develop stitch technique to strengthen composites

The newest aircraft flying through the sky are primarily made up of composites. These materials are extremely light and durable making them the perfect choice for airplanes. They can reduce the overall weight of an aircraft by upwards of 20 percent over aluminum-bodied planes. With the push to lightweight and make planes more energy efficient, researchers are looking for ways to improve material strength.

Illustration courtesy of Christine Daniloff/MIT

One of the limitations of composites is they are surprisingly vulnerable. Composite layers subject to even the smallest impact can break apart and fracture, which can be catastrophic mid-flight.

Roberto Guzman led the work as an MIT postdoc in the Department of Aeronautics and Astronautics (AeroAstro) and the study’s co-authors include AeroAstro professor Brian Wardle and researchers from the Swedish aerospace and defense company Saab AB.

MIT aerospace engineers have developed a way to bond composite layers together. This new method will make composite materials substantially stronger and more resistant to damage. Their results are published this week in the journal Composites Science and Technology.

The engineers used carbon nanotubes to fasten layers of  composite material together. The team then embedded the carbon nanotube structure within a glue-like polymer matrix and pressed the matrix between layers of carbon fiber composites. The nanotubes, resembling tiny, vertically-aligned stitches, worked themselves within the crevices of each composite layer, serving as a scaffold to hold the layers together.

“Size matters, because we’re able to put these nanotubes in without disturbing the larger carbon fibers, and that’s what maintains the composite’s strength,” Wardle says. “What helps us enhance strength is that carbon nanotubes have 1,000 times more surface area than carbon fibers, which lets them bond better with the polymer matrix.”

The team found that the stitched composites were 30 percent stronger than traditional materials and withstood greater force before breaking apart.

The improvement may lead to stronger, lighter airplane parts, particularly in those that require nails or bolts, which can crack conventional composites, explains Guzman.

“The strength enhancements suggest this material will be more resistant to any type of damaging events or features,” Wardle says. “And since the majority of the newest planes are more than 50 percent composite by weight, improving these state-of-the art composites has very positive implications for aircraft structural performance.”

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