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Shape-Shifting Carbon Composites Could Save Fuel

Airbus is developing carbon materials that change in response to heat and air pressure, possibly making aircraft simpler and lighter.

Even small reductions in fuel consumption can save airlines millions of dollars.

Airbus and researchers at MIT are developing shape-shifting materials that could make aircraft simpler and lighter, potentially saving fuel. Made of carbon fiber composites, the materials shift between two or more shapes in response to changes in heat, air pressure, or other environmental factors. They can be integrated into aircraft easily, replacing the need for more complex hydraulic actuators, motors, and hinges. The first application might be in a jet engine’s air intake valve, which needs to adjust as the plane changes altitude.

A time-lapse photograph shows a carbon fiber composite bending in response to heat.

Shape-changing materials are nothing new. Materials that corkscrew, bend, grow, and shrink in response to heat and other stimuli, such as light and electricity, have been around for decades. You can find them in cars, airplanes, robots, and medical implants. But their use has been limited in aircraft because many can’t handle the conditions planes are exposed to, such as extreme temperature changes, says Christophe Cros, a technology program leader at Airbus.

The MIT approach has a number of advantages, Cros says. First, most shape-shifting materials don’t use carbon composites, which are common in aircraft because of their light weight and high strength.

And though others have worked on carbon composites that can respond to a specific stimulus such as heat, Cros says in the new approach, the carbon composites can be paired with a variety of shape-shifting materials that respond to different environmental triggers. This makes it possible to choose a specific trigger that won’t be accidentally set off in the wrong conditions, such as a hot day, he says. Another advantage to the new approach is that it doesn’t require the electrical connections some other shape-changing composites need.

Skylar Tibbits, director of MIT’s Self-Assembly Laboratory, begins with novel carbon fiber composites developed by the startup Carbitex, based in Kennewick, Washington. Most carbon fiber composites are rigid: the glue that holds the fibers together, known as matrix, doesn’t allow them to bend. But Carbitex has developed a variety of matrix materials that impart a range of properties. Some result in carbon composites that are floppy like a cotton sheet. Others are springy, like a sheet of metal.

Tibbits then uses a 3-D printer to apply materials that are known to shrink or grow under certain conditions. As they change, they force the carbon composite on which they’re deposited to bend or twist in various ways, depending on the pattern produced by the printer. He and his colleagues are developing design software that simulates the way different patterns of these materials, printed onto different kinds of composite materials, will behave under different conditions.

So far, Tibbits has demonstrated materials that respond to light, water, and heat. But he says it should be possible to make ones that respond to air pressure and other stimuli. 

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