United States Department of Transportation
i
Bonded Repairs of Composite Wing Panel Structure: Phase 3, Bonded Repair Size Limits Study for Solid Laminates with Double-Sided Scarf Panels
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2022-06-01
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[PDF-36.10 MB]
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Edition:Final
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Abstract:In a collaborative effort, the Federal Aviation Administration (FAA) and The Boeing Company are assessing bonded repair technologies of composite panels representative of transport airplane wing-structures through test and analysis using the FAA’s Aircraft Beam Structural Test (ABST) fixture. Emphasis has been placed on investigating methods and tools used to conduct analysis and predict structural performance of bonded repairs and those used to monitor and evaluate repair quality and durability over the life of the part. This project was carried out in a phased approach. Current phase 3 efforts support bonded repair size limit (BRSL) studies and methods used to predict the limit-load residual strength for failed repair scarf configurations. Full-depth, half-depth, and double sided scarfs were inserted in carbon-fiber-reinforced polymer (CFRP) panels having an 18-ply quasi-isotropic layup. The panels were attached as top-side components (e.g., skins) of a cantilevered, 24-inch- wide by 40-inch-long wingbox structure. These panels were subjected to constant-moment loads either tested quasi-statically to failure or subjected to fatigue before loading them to failure. The applied fatigue loading conditions simulated normal operational strain levels for transport-category wing panels for 165,000 cycles, which is approximately equal to three design service goals (DSGs). Results for full-depth scarf and half-depth scarf configurations is documented in a companion technical report (DOT/FAA/TC-21-27). This report focuses on panels with double-sided scarf configurations, where two panels had no repair patches and three panels had single-sided repair patches representing a half-depth scarf. In general, methods under development for BRSL residual strength predictions correlated well with test results. At low strain survey load, the strains in the panel with double-sided scarf and single-sided patch were comparable to the half-depth scarf panels. However, the single-sided repair patch was not effective in restoring strength. During residual strength tests, the repair patch experienced early bondline failure from high peel stresses caused by bending eccentricity. While these results provide valuable insights to the residual strength behavior of CFRP panels with various scarf configurations, caution must be exercised in their direct application to real structure having reinforcing substructure.
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