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Bolted field repair techniques have been developed for AV-8B and F-18 aircraft graphite/epoxy monolithic wing skin laminates up to 12.7 mm (0.5 in.) thick with through-the-thickness damage near and at substructure. Damage sizes to 101.6 mm (4.0 in.) in diameter have been repaired by mechanically fastening a titanium patch to the laminate using blind fasteners in single shear. Repairs were performed with access only to outer surface. Allowables needed for repair design were developed by test for strains at the edge of damaged hole, tension/bearing interaction, and joint shear strength. The capability of an interactive bolted repair analysis computer program (BREPAIR) is also presented. The BREPAIR can define patch geometry and fastener requirements in considerably less time than conventional finite element modeling. Strain predictions correlate well with experimental results. Static tension tests verified that the mechanically fastened repair patch restores the strain capability of the damaged skin to a gross failure strain that exceeds the 4000 μmm/mm design goal. Residual strength tests after four lifetimes of spectrum fatigue also exceed the design goal strength.
bolted joints, field repair, composite repair, composite materials, graphite/epoxy, wing structures
Technical specialist, McDonnell Douglas Corporation, McDonnell Aircraft Company, St. Louis, Mo.
Lead engineer, McDonnell Douglas Corporation, McDonnell Aircraft Company, St. Louis, Mo.
Aerospace engineer, Naval Air Development Center, Warminster, Pa.