Carbon Fiber Composites in Aviation
As the aviation industry attempts to reduce fuel costs by reducing the weight of aircraft, lightweight composite materials with extraordinary strength continue to be developed and improved. Carbon-fiber composites have been created that can match the strength of titanium and aluminum, while being much lighter in weight, to the extent that aircraft using these composites materials can weigh of up 20 percent less than they would otherwise. Both the Boeing 787 and Airbus A380 contain carbon-fiber composites.
Researchers looking at creating even stronger and lighter materials are working with carbon fibers that are coated with carbon nanotubes. When arranged in specific configurations, these tiny tubes of crystalline carbon are hundreds of times stronger than steel while being only around one-sixth of the weight of steel. Until recently scientists faced the problem that when growing carbon nanotubes on carbon fibers the underlying fibers have lost some of their strength. The root cause of this fiber degradation has been identified by a team of researchers from MIT, and techniques have been devised to preserve the strength of these fibers.
Associate professor of aeronautics and astronautics at MIT, Brian Wardle, notes that up until now one part of the material was being improved at the expense of the underlying fiber, but the new technique does away with this trade-off situation, with both the carbon nanotubes and carbon fibers maintaining their integrity.
Upon visiting carbon-fiber production plants in Germany, Japan and Tennessee, researchers found that the manufacture process required fibers to be stretched close to breaking point and heated to high temperatures, which had not been replicated in laboratory conditions. Upon replicating these conditions in the laboratory and carrying out a series of experiments it was discovered that the main cause of fiber degradation was a mechanochemical reaction resulting from a lack of tension when heating carbon fibers at a high temperature.
Having identified the problem, researchers coated the carbon fiber with a layer of alumina ceramic to ensure the iron catalyst would stick to the fiber but not degrade it. However, the alumina kept flaking off. Undaunted, the research team developed a polymer coating with both hydrophilic and hydrophobic components and coated the fibers with it, allowing them to grow nanotubes without damaging the fiber. Further experiments resulted in growing nanotubes at lower temperatures, thereby avoiding damage to the underlying fiber. Patents have been filed for the nanotube growing techniques and hopes are high that these new composite materials will have a wide range of applications in the aerospace industry.