Composite Repairs of Fatigue-damaged Aluminum Panels

Composite repairs of fatigue-damaged metallic aircraft structures provide cost effectiveness and sound structural integrity. A series of NASTRAN Finite Element (FE) analyses was performed on hybrid mathematical models with crack elements to determine stress intensity factors (SIFs). Crack growth analysis was performed to determine repair durability strength. A coupon test specimen was designed and prepared of 7075-T6 aluminum. A 19.05-mm (0.75-in.) long through-the-thickness center crack was introduced in the test panel and then repaired with a 190.5-mm (7.5-in.) long by 63.5-mm (2.5-in.) wide composite patch. The repair patches were cured with boron/epoxy (B/Ep) and graphite/epoxy (Gr/Ep) composites in [0{3}+/-45/02]s and [O{10}] ply orientations. The repair durability tests were performed. Composite repair was performed on a fatigue-damaged access door of an aircraft. Cost savings by the composite repair, compared to conventional metallic repair, were ten times in material cost and five times in design/installation labour.