MIT researchers’ process makes aerospace-grade composites sans oven, autoclave
Carbon nanotube film plays key role in bonding and removing voids between composite layers.
“Now we have this new material solution that can provide on-demand pressure where you need it,” said Brian Wardle, professor of aeronautics and astronautics at MIT. “Beyond airplanes, most of the composite production in the world is composite pipes, for water, gas, oil, all the things that go in and out of our lives. This could make making all those things, without the oven and autoclave infrastructure.”
Key to the MIT-developed process are razor-thin sheets of carbon nanotubes. To heat and fuse the layers of composite parts, for example, the method wraps them in a shroud of nanotubes, to which an electrical current is applied (i.e conductive curing). According to the research team, this out-of-oven (OoO) technique made composites as strong as those from conventional airplane manufacturing ovens, but using only 1 percent of the energy. The next challenge, Wardle said, was replicating the high pressures of an autoclave.
“There’s microscopic surface roughness on each ply of a material, and when you put two plys together, air gets trapped between the rough areas, which is the primary source of voids and weakness in a composite,” Wardle says. “An autoclave can push those voids to the edges and get rid of them.”
To create Out-of-Autoclave (OoA) composites, the researchers again employed carbon nanotubes but this time as nanoporous networks (NPN) – ultra thin film of carbon nanotube arrays. The researchers theorized that the gaps between the vertically aligned microscopic tubes or capillaries, based on their geometry and surface energy, could generate pressures locally that were larger than those produced holistically by an autoclave. Placing the NPN film between composite layers, therefore, would draw composite layers together and forcing out voids during the curing stage.
“We found that our out-of-autoclave composite was just as strong as the gold-standard autoclave process composite used for primary aerospace structures,” Wardle says.
To date, the researchers have experiment with samples are only centimeters wide; the next step will to scale the process up to commercially viable dimensions, which will require large sheets of carbon nanotube film.
“There are ways to make really large blankets of this stuff, and there’s continuous production of sheets, yarns, and rolls of material that can be incorporated in the process,” Wardle said, adding that the plan is also to explore different formulations of nanoporous films to pressurize and bond other high-performance materials.
The researchers’ method is detailed in a paper published in the journal Advanced Materials Interfaces. Wardle’s co-authors on the paper were lead author and MIT postdoc Jeonyoo Lee, and Seth Kessler of Metis Design Corporation, an aerospace structural health monitoring company based in Boston.
Their research was supported, in part, by Airbus, ANSYS, Embraer, Lockheed Martin, Saab AB, Saertex, and Teijin Carbon America through MIT’s Nano-Engineered Composite aerospace Structures (NECST) Consortium.