Material Approaches to Mitigate Gap Filler Cracking

Development of crack resistant conductive gap-fillers fits within the Air Force’s goal of investing in low observable maintenance improvements that will decrease sustainment costs and reduce aircraft downtime. Commercially available gap-fillers are initially effective, but performance degrades under thermal and mechanical fatigue resulting in microcracks within the matrix. Mitigation of cracking will be approached by the development of high endurance elastomeric resins capable of infusing into existing treated gaps in situ. While mitigation of cracking with currently approved gap-fillers is a prudent step in solving the problem, development of new elastomeric matrix resins is also needed to prevent the need for mitigation. A parallel approach will involve the development more durable elastomeric matrix resins capable of delivering the required conductivity and fatigue resistance. The combination of mechanical and thermal fatigue generates the most aggressive stresses for gap-fillers on aircraft, where temperatures within the range of -65oF to 250oF are experienced. These stresses occur as a result of differential thermal expansion and modulus changes in the gap-filler material. Experiments will be conducted to replicate these stresses in the laboratory in order to determine the effect of crack mitigation techniques on extended durability. The project team assembled includes a major gap-filler producer and airframe manufacturers. BENEFIT: Mitigation of cracking within gap-fillers will benefit many modern fighter/bomber platforms by reducing maintenance costs and downtimes. Commercial aircraft could potentially benefit as well from the development of high endurance sealant matrix materials.