Fundamentals of Noncuring Sealants for Aircraft Fuel Tanks

The need for efficient space utilization in military aircraft has led to the use of wing and fuselage cavities as fuel tanks. Of the three methods of sealing these cavities filleting, faying, and channel, channel sealants are the least understood and have the most contrast between behavior and requirements. Potential failure mechanisms were identified against the thermal, chemical, and physical aspects of the fuel tank environment. Thermal degradation, low temperature embrittlement, thermal expansion, and viscosity reduction were mechanisms associated with the -54 C to 177 C temperature range. Hydrolysis, oxidation, closed system reversion, and crosslinking were associated with the chemical aspect. Fuel swelling of the sealant, extraction by fuel, system pressure, vibration, shear, and adhesioncohesion were associated with the physical aspect. Selected polymers with a wide variety of formulating ingredients were evaluated as channel sealants in laboratory-sized test apparatus to confirm the suspected failure mechanisms. The results have been digested as engineering principles that govern the behavior of channel sealants. Application of these principles resulted in some immediate benefits and a basis for long range sealant development.