United States Department of Transportation
i
Bonded Repairs to Composite Wing Panel Structure: Phase 3—Bonded Repair Size Limits Study for Solid Laminates with Full-Depth and Partial-Depth Scarf Configurations
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2021-07-01
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[PDF-46.67 MB]
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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 over the life of the part. This project is carried out in a phased approach where phase 1 was fixture development and verification. Phase 2 was the initial baseline testing that verified the analysis models and provided an initial reference point for inspection and monitoring systems used to detect and track damage formation. This report discusses the recent third-phase efforts to support bonded repair size limit (BRSL) studies and methods used to predict the limit-load residual strength for a failed scarfed repair in solid composite laminates with full-depth and partial-depth scarf configurations. 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 tested either quasi-statically loaded to failure or subjected to fatigue before loading them to failure. The applied fatigue loading conditions simulated highest operational strain levels for transport-category wing panels for 165,000 cycles, which is approximately equal to three design service goals (DSGs). The test and analysis results revealed a significant benefit of partial-depth scarfs over full-depth scarfs. In addition, there was no debit in strength due to fatigue in both type of panels tested. For both full-depth and partial-depth scarf configurations, the methods under development for BRSL residual strength predictions correlated well with test results. Follow-on efforts are focused on panels with double-sided scarf configurations, which will be documented in a companion technical note.
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