Treatments for Crack Propagation in Metal Aircraft Parts

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Microelectronics; Advanced Materials; Advanced Infrastructure & Advanced Manufacturing; Sustainment & Logistics The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. OBJECTIVE: Develop and demonstrate ground support equipment capable of performing in-place repair of structural components with stress-induced cracks without removing component from aircraft. DESCRIPTION: The lifetime of metal aircraft parts is limited by stress-induced crack initiation and propagation of these cracks until part failure results. Often these parts are difficult to replace, and methods to extend the useable service life of aircraft parts would be advantageous. Research on treatments to inhibit growth of cracks after initiation has shown promise. Practical applications of this research are sought to extend aircraft part lifetime while maintaining dimensional tolerances and mechanical properties of the components. The ability to perform crack arrest repairs on parts without removing them from the aircraft will drastically reduce depot visits and increase aircraft availability. As such, the technology sought must be portable, and enable application of the repair in space-constrained areas of the aircraft. The desired characteristics of the developed technology include: (1) ability to apply repair with the part in a loaded (stressed) state, (2) maintains the designed functionality of the treated part without adversely impacting its lifetime in any other manner (e.g., must not induce galvanic corrosion due to application of dissimilar metal), (3) minimizes pre-repair part conditioning (e.g., as much as possible, leave protective coatings in place), (4) does not generate sparks, (5) must not have wireless emissions (no WIFI, Bluetooth, etc.), and (4) minimized repair time. Repair of aluminum alloys are of primary interest, but also steel. The successful technology must not require line power exceeding common voltages (120/240 V) and must minimize hazmat footprint. PHASE I: As this is a Direct-to-Phase-II (D2P2) topic, no Phase I awards will be made as a result of this topic. To qualify for this D2P2 topic, the Government expects the applicant(s) to demonstrate feasibility by means of a prior Phase I-type effort that does not constitute work undertaken as part of a prior or ongoing SBIR/STTR funding agreement. To demonstrate that the technology is ready for a D2P2, the applicant must be able to show they have a plan, or technology, that can repair the cracks in a rapid-repair capacity. This will show the technology is ready for prototype to fit the specific military needs based on aircraft parts, metals, and environments. PHASE II: Awardee(s) will develop and demonstrate a prototype system that meets topic objective. The prototype demonstration should illuminate the ability of the technology to rapidly repair stress-induced cracks without removal from the aircraft, and address other desired characteristics (either in practice, or with a plan for future modification/development). Finally, effort will provide cost projection data to substantiate the design, performance, acquisition, and life cycle costs. PHASE III DUAL USE APPLICATIONS: This topic is provided by AFGSC's Commercial Capabilities Integration and Transition Branch at the AFGSC/A5N branch. This branch is deliberately resourced and staffed exclusively to ensure R&D efforts are integrated into AFGSC programs of record and have senior leader sponsorship and POM/Programming advocacy among AFGSC corporate processes. There are resources set aside to effectively transition this effort into a Phase 3 follow on if the Phase 1 and Phase 2 efforts are successful. REFERENCES: C.M. Barr, T. Duong, D.C Bufford, et al. Autonomous healing of fatigue cracks via cold welding. Nature 620, 552 556 (2023). https://doi.org/10.1038/s41586-023-06223-0 J. Huang, and H. Cardenas. Fatigue Crack Arrest in Mild Steel via Iron Electroplating. Materials Sciences and Applications, 12, 484-503, 2021. doi: 10.4236/msa.2021.1211032. C. R. Fisher, H. B. Henderson, M. S. Kesler, et al. Repairing large cracks and reversing fatigue damage in structural metals, Applied Materials Today, Volume 13, 2018, Pages 64-68, ISSN 2352-9407 R. Jones, A.A. Baker, N. Matthews, V. Champagne. Aircraft Sustainment and Repair, Butterworth-Heinemann, 2017, ISBN 008100544X, 9780081005446 R. Jones, A. A. Baker, Bonded Repair of Aircraft Structures, Springer, Netherlands, 2012. ISBN:9789400927520, 9400927525 H. J. Gover, Fatigue of Aircraft Structures, Defense Technical Information Center, AD0660529. 1966. https://apps.dtic.mil/sti/pdfs/AD0660529.pdf"; KEYWORDS: crack mitigation; crack propagation; crack arrest; aircraft fatigue failure; crack closure