Title: Feasibility Study of Fiber-Oriented Scarf Repairs for Carbon Fiber Reinforced Composite Panels

Authors: Reewanshu Chadha, John G. Bakuckas, John Z. Lin, Michael Fleming, Christopher Brooks-Jr., Erick Espinar-Mick

DOI: 10.33599/nasampe/s.24.0118

Abstract: "The Federal Aviation Administration and The Boeing Company have been investigating the safety and structural integrity issues of bonded repair technology. Efforts are focused on testing and analyzing bonded repairs to 101.6-cm x 61-cm flat carbon fiber reinforced composite panels representative of wing skin using the Aircraft Beam Structural Test 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 scarfs are machined in such a way that only plies in the fiber directions are overlapped. 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 via the use of 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 in a similar fashion as the traditional scarf repair panels, but due to the lack of smooth tapering and abrupt termination of ply overlapping in the transverse direction, there was 13% and 4% reduction in strength when compared to tapered and stepped scarf repair panels respectively. However, fiber-oriented scarf repairs did provide the benefit of precision in material removal and 40% reduced repair footprint. Analytical methods under development for bonded repair ultimate tensile strength predictions correlated well with test results. "

References: 1.Pitanga, M. Y., Cioffi, M. O. H., Voorwald, H. J. C. and Wang, C. H., ""Reducing repair dimension with variable scarf angles."" International Journal of Adhesion and Adhesives 104 (2021) [https://doi.org/10.1016/j.ijadhadh.2020.102752]. 2.Schmutzler, H., & Höfener, M. ""Automated Scarfing: A Prerequesite for Future Structural CFC Repairs. "" North Atlantic Treaty Organization Science and Technology Organization, 2018. 3.Pierce, R. S. and Falzon, B. G., ""Modelling the size and strength benefits of optimised step/scarf joints and repairs in composite structures."" Composites Part B: Engineering 173 (2019) [https://doi.org/10.1016/j.compositesb.2019.107020]. 4.M. Niedernhuber, J. H. ""Fiber-oriented repair geometries for composite materials."" Composites Part B: 327-337, 2016 [https://doi.org/10.1016/j.compositesb.2016.03.027]. 5.Chadha, R., Bakuckas Jr., J. G., Fleming, M., Lin, J., & Korkosz, G. ""Airframe beam structural test (ABST) fixture—capabilities description and user manual."" U.S. Department of Transportation Federal Aviation Administration DOT/FAA/TC-TN19/7, 2019. 6.Neel, R. J., Chadha, R., Bakuckas Jr., J. G., Fleming, M., Lin, J., & Espinar-Mick, E. ""Bonded Repairs to Composite Wing Panel Structure: Phase 2, Baseline Study."" U.S. Department of Transportation Federal Aviation Administration."" DOT/FAA/TC-21/17, 2021 [https://rosap.ntl.bts.gov/view/dot/61458/dot_61458_DS1.pdf]. 7.Neel, R. J., Chadha, R., Bakuckas Jr., J. G., Lin, J., Fleming, M., & Espinar-Mick, E. ""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."" U.S. Department of Transportation Federal Aviation Administration. DOT/FAA/TC-21-27, 2021 [ https://rosap.ntl.bts.gov/view/dot/60942/dot_60942_DS1.pdf]. 8.Hashin, Z. "Failure Criteria for Unidirectional Fiber Composites." Journal of Applied Mechanics 47 (1981): 329-334 [https://doi.org/10.1115/1.3157744].

Conference: SAMPE 2024

Publication Date: 2024/05/20

SKU: TP24-0000000118

Pages: 16

Price: $32.00