Bonded boron/epoxy doublers are an alternative method vs riveted metal doublers for repair and reinforcement of metallic aircraft structures. They eliminate new holes and provide cost and/or performance advantages for many applications. Over 6,500 boron doublers are flying on military aircraft, mostly in Australia and the U.S.A., and their use is increasing. Commercial aircraft, which are also aging, are beginning to use this technology -- about 230 doublers are flying, either as demonstration “decals”, structural enhancement, or minor repairs.
This paper describes the commercial applications and the major U.S. military ones. The doubler installation process is also described. One documentation of its reliability is the experience on the F-111: no debonds on over 800 doublers in 20 years of use.
This paper also presents the results of an extensive test program sponsored by Textron at Boeing: 110 ultimate tensile strength and 143 fatigue tests of boron/epoxy doublers bonded to 7075-T6 aluminum with simulated cracks.