MIT aerospace engineers have successfully designed a carbon nanotube (CNT) film that is capable of heating and solidifying a composite without requiring large ovens. The heated film causes solidification of the polymer, when electric power is supplied and it is wrapped over a multilayer polymer composite.
Composite materials that find applications in fuselages and aircraft wings are produced in huge industrial-sized ovens. A solid, durable material is formed by blasting several multiple polymer layers with temperatures up to 750°F. The drawback of this technique is that a significant amount of energy is required for heating the oven, the surrounding gas and the composite itself.
The team discovered that the composite formed by the CNT film was as robust as those produced in ovens with just 1% of the energy usage. The film testing was carried out on a carbon-fiber material normally used in aircraft parts.
According to Brian L. Wardle, an associate professor of aeronautics and astronautics at MIT, this new technique could provide direct, energy savings for manufacturing almost any industrial composite.
Typically, if you’re going to cook a fuselage for an Airbus A350 or Boeing 787, you’ve got about a four-story oven that’s tens of millions of dollars in infrastructure that you don’t need. Our technique puts the heat where it is needed, in direct contact with the part being assembled. Think of it as a self-heating pizza. … Instead of an oven, you just plug the pizza into the wall and it cooks itself.
Brian L. Wardle
Associate Professor of Aeronautics and Astronautics at MIT
Wardle added that the CNT film is extremely light and after integrating the polymer layers underneath, the film blends with the composite. The film is just a fraction of the diameter of a human hair and hardly adds any weight.
Experimentation with CNT films has been carried out by Wardle and his colleagues in the last few years for the purpose of de-icing airplane wings.
The team formulated a method to develop an aligned carbon nanotube film comprising tiny crystalline carbon tubes, which stand erect similar to trees in a forest. Using a rod, the researchers rolled the “forest” flat, forming a dense aligned carbon nanotube film.
While conducting experiments, Wardle and his team combined the film into airplane wings through traditional oven-based curing techniques. The researchers demonstrated that heat was generated by the film on application of voltage, thus averting ice formation.
From the deicing tests, the researchers felt that if heat generation was possible by the CNT film, why it could not be used for creating the composite itself.
In preliminary experiments, the team studied the capability of the film to fuse two kinds of aerospace-grade composites used normally in fuselages and aircraft wings. The material normally has around 16 layers and is cross-linked or solidified in a high-temperature industrial oven.
The size of the CNT film developed was around that of a Post-It note, and the film was positioned over a Cycom 5320-1 square. Electrodes were connected to the film and a current was applied to heat the film and the polymer below in the Cycom composite layers.
The team quantified the energy needed to cross-link, or solidify the carbon fiber and polymer layers and determined that the CNT film used 1% the electricity needed for conventional oven-based methods for composite curing. In both techniques, composites were produced with similar characteristics, for instance, cross-linking density.
According to Wardle, the results inspired the team to further test the CNT film. Since the fusing temperatures are different for individual composites, the researchers wanted to test if the CNT film was actually capable of withstanding the heat.
“At some point, heaters fry out,” Wardle says. “They oxidize, or have different ways in which they fail. What we wanted to see was how hot could this material go.”
In order to test this, the team evaluated the ability of the film to produce increasing temperatures and determined that the temperature that the film could withstand was above 1,000°F. However, even the highest temperature aerospace polymers needed temperatures up to 750°F for solidification.
“We can process at those temperatures, which means there’s no composite we can’t process,” Wardle says. “This really opens up all polymeric materials to this technology.”
The group is collaborating with industrial partners in order to scale up the technology for producing huge composites that can help manufacture airplane wings and fuselages.
“There needs to be some thought given to electroding, and how you’re going to actually make the electrical contact efficiently over very large areas,” Wardle says. “You’d need much less power than you are currently putting into your oven. I don’t think it’s a challenge, but it has to be done.”
According to Gregory Odegard, a professor of computational mechanics at Michigan Technological University, the carbon nanotube film of the team may help in enhancing the effectiveness and quality of fabrication processes for large composites, for instance, wings on commercial aircraft. The novel approach may also pave the way for smaller firms, which cannot afford huge industrial ovens.
"Smaller companies that want to fabricate composite parts may be able to do so without investing in large ovens or outsourcing," says Odegard, who was not involved in the research. "This could lead to more innovation in the composites sector, and perhaps improvements in the performance and usage of composite materials."
Airbus Group, Boeing, Embraer, Lockheed Martin, Saab AB, TohoTenax, ANSYS Inc., the Air Force Research Laboratory at Wright-Patterson Air Force Base, and the U.S. Army Research Office partly funded the research.
The findings of the research team, including MIT graduate students Jeonyoon Lee and Itai Stein and Seth Kessler of the Metis Design Corporation, have been published in the journal ACS Applied Materials and Interfaces.