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Bonded Repairs to Composite Wing Panel Structure: Phase 4, Feasibility Study of Panels with Fiber-Oriented Scarf Repairs
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2024-11-01
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[PDF-14.45 MB]
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Abstract:The Federal Aviation Administration (FAA) and The Boeing Company have investigated safety and structural integrity issues of bonded repair technology. Efforts are focused on testing and analyzing bonded repairs to 40-in x 24-in flat carbon fiber-reinforced composite panels representative of wing skin using the Aircraft Beam Structural Test (ABST) fixture. As part of this program, a feasibility study was conducted to determine the effectiveness of fiber-oriented scarfing in restoring the strength of repaired panels. The term feasibility is used here to assess the practicality of a concept proposed in another study. Fiber-oriented scarf repair is bonded in a way that for every layer, plies are not overlapped in the perpendicular direction to the fiber. As compared to traditional circular scarf repair, fiber-oriented scarf repair has the same number of plies but uses a smaller footprint, reduces the technician skills required to fabricate the scarf using automation, and improves ergonomics and efficiency. Repaired panels with fiber-oriented, tapered, and stepped scarfs were considered in this study. In general, all repair configurations were able to restore strength beyond notched structure capability, which is defined as the strength of a laminate containing a small hole or small damage and is often considered a critical sizing component for primary structures. All fiber-oriented scarf repair panels failed similarly as the traditional scarf repair panels. However, due to the lack of smooth tapering and abrupt termination of ply overlapping in the transverse direction, there was a reduction in strength when compared to tapered (13%) and stepped scarf (4%) repair panels. Fiber-oriented scarf repairs did provide the benefit of precision in material removal and a 40% reduced repair footprint. Analytical methods under development for bonded repair ultimate tensile strength predictions correlated well with test results.
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