The blade shells and shear web were infused with Arkema’s Elium® reactive thermoplastic resin system, a liquid resin that’s processed like a thermoset, but cures at room temperature. According to Berry, the prototype was the first blade produced in the U.S. using a thermoplastic resin system. The resin speeds up production. For example, the team did the shear web infusion using the Elium 188 system and got a wet-out of the entire part in about 30 minutes. The shear web was demolded and had its full-strength properties in only three hours – much faster than thermoset materials, according to the YouTube video.
Another innovation is specialized sizing – a coating on the fiberglass itself – that is fully compatible with the resin system. The sizing, provided by Johns Manville, helps ensure that the resin and fibers work well together and that the load transfers to the reinforcement so the composite doesn’t fail at the interface.
In addition, the blade features a pultruded spar cap produced by Strongwell that uses Oak Ridge National Laboratory’s low-cost carbon fiber combined with Huntsman’s polyurethane resins. “The larger and longer the blade gets, the more it needs very stiff materials and carbon fiber becomes a more attractive material,” says Berry. The blade also incorporates recycled PET foam from Creative Foam as a core material, so there’s post-consumer material in the blade itself.
In addition to the companies already named, other partners on the project include TPI Composites Inc., DowAksa USA, Chomarat USA, Composites One, SikaAkson and Chem-Trend. The prototype is just the start of the group’s work, said Berry. “We’re showing what we can do, but we have a lot more work to do,” he said. “Our ultimate goal is to commercialize this technology.”
The Disrupter: NASA’s Structural Carbon Nanotubes
Broader Implications: The potential to save weight, reduce mass and improve performance in aerostructures.
In the aerospace industry, composite nanotechnology has long been a topic of great interest. In 2012, a study from the U.S. Army Corps of Engineers showed that it is possible to develop carbon nanotube fibers with tensile strengths as high as 60 Gigapascals (GPa) – which is more than 10 times as high as conventional intermediate modulus carbon fibers. Other NASA analyses have shown that composites using carbon nanotube reinforcements could lead to a 30 percent reduction in the total mass of a launch vehicle.
Earlier this year, a composite overwrapped pressure vessel (COPV) on a payload in NASA’s SubTec-7 mission flight became the first structural component made with carbon nanotubes flight tested by NASA. To industry outsiders, this raised an interesting question: If composite nanotubes are so strong, what was holding NASA back from flight testing them in a structural component? According to Mike Meador, program element manager for lightweight materials and manufacturing at NASA’s Glenn Research Center in Cleveland, the answer is that historically, carbon nanotubes have not been available for testing in “useful formats” like fabrics or fibers.