In aerospace, the push for lighter weight aircraft has increased the need for better composites and multi-material joining solutions, says Chuck Zhang, CHMI’s director and the Harold Smalley Professor in Georgia Tech’s H. Milton Stewart School of Industrial and Systems Engineering. Airlines know how to repair and maintain older, mostly metal aircraft like the 737 and 757. But they lack the expertise required for the newer Boeing 787 and Airbus A350, in which more than half of the structure by volume is composite materials. Many of these repairs involve aircraft sections where composite components are used in conjunction with components manufactured from other materials.

“People in the aircraft maintenance field tell me that they have very limited knowledge of how to repair these. If there’s minor damage, they can patch it, but if there’s major damage – like a big hole in the wing or fuselage – they normally have to go back to the OEMs,” Zhang says. That can quickly drive up the airline’s repair and maintenance costs.

Manufacturers of these aircraft have their own concerns about multi-material components. For example, when they drill holes and use mechanical fasteners to join composite materials with aluminum or steel, the composite materials may get damaged and lose strength.

Zhang says that CHMI researchers originally thought their focus would be on creating advanced adhesives that would eliminate the need for mechanical fasteners. But the airline industry representatives pointed out that the FAA requires both adhesive and mechanical fastening for multi-material joints. So, one area that CHMI research teams could focus on is developing computational models, process control and non-destructive testing methods that could help change those requirements. They might test adhesives and processes on a repair for subscale, such as a 3 x 3-foot composite/metal structure, and then use modeling to predict how feasible this solution would be on a larger scale.

CMHI researchers and their industry partners also hope to find ways to increase automation of the composite/metal joining process during both manufacturing and repair. This will be easier to achieve in the manufacturing plant, where work can be standardized, than in the field, where repairs to a composite or multi-material aircraft may be required in many places.

For instance, the researchers might study robots like those developed by Lufthansa Technik as part of its CAIRE Project (Composite Adaptable Inspection and Repair). The mobile robots can cling to aircraft wings and fuselages to inspect and repair the composite structures by scanning and recording damages, removing damaged materials and producing customized repair layers, says Zhang.