The center establishes procedures and protocols for manufacturing testing that are the equivalent of materials specifications. An analogy is the industry standard 20214T3 aluminum specification that has its roots in the material used in World War II. “We want a testing regime to be of a similar spec,” Tomblin says. Composites developed in the early- and mid-1990s that are now common can be characterized by material and specification. Procedures for manufacturing with them can be certified by an equivalency process.
“Changing materials is a big deal” because of the time and testing required for certification, Tomblin says. For that reason, Lockheed Martin's F-22 was built using 25-year-old material and the F-35 uses the same material, he says. The composite material from the 777's empennage was accepted for the 787.
NCAM is trying to break down certification and time elements so baseline performance levels of new materials can be established quicker. Their goal is to drop them by 1/6th, meaning a three-year schedule to achieve certification can be dropped by six months.
One of NIAR's research efforts is on improving lightning protection systems for composite skins. Boeing's method is proprietary, but involves an interweave of conductive wires in the outermost plies of the fuselage. For the B-2 bomber, the protection system was actually part of the radar imaging-resistant coating. If the conductive wires are buried any deeper than the outer layer they will be ineffective, says NIAR senior research engineer Lamia Salah, who leads its advanced materials laboratory.
NIAR is working on electromagnetic interference-resistant nano skins that can be applied directly onto composite structures as part of the RTI process. The skins would provide lightning protection and serve other purposes for military aircraft.
Such experiments hold promise for reducing composite manufacturing costs, says Tomblin. Besides the cost of buying the lightning-protective mesh itself, there is the cost of integrating it into a structure, he says. Applying a nano skin as just another layer in a resin transfer molding takes out this middle step.