Vitrimer Patches to Repair Composite Parts with a Complex Shape in a Contested Environment

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials;Sustainment OBJECTIVE: Determine the feasibility of using vitrimer repair patches for repairing composite damage on a contoured surface in a contested environment. DESCRIPTION: Repairing composites damaged on a contour is always a challenge. This is especially true when the fleet is forward deployed and operates in a contested environment. Usual go-to repair is a wet-layup patch. However, using wet layup patches results in a strength knockdown. The Navy is seeking a robust vitrimer resin based solution that can be deployed with the fleet and will be used to perform repairs in the theater, that will restore the full strength of the composite part. Vitrimers are a relatively new class of resins developed over the last decade which has dynamic chemistry in which covalent bonds are exchanged and rearranged by providing stimuli such as heat. Referred to as reversible thermosets, these polymers have thermoset properties below the glass transition temperature (Tg) yet behave like a thermoplastic at elevated temperatures, above the Tg. Tg can currently be tailored between 80 C to 180 C. However, the chemistry and the resulting Tg are an area of active research. Kits can be developed as flat patches and contoured to shape as needed in the theater. These contoured patches can be cured on the part or secondarily bonded using traditional epoxy vitrimer/epoxy based resins. These late resins can provide bond strength at least as good or better than traditional epoxy adhesives but also can be cleanly removed as needed by applying heat. PHASE I: Identify suitable vitrimer resin pre-pregs and demonstrate its feasibility to be used for repair. Through suitable experimental campaign, map its formability and mechanical properties. In Phase I any limitations in obtaining tight tolerances and any property degradation during reforming the vitrimer patches should be identified. Potential methods to join it to a carbon/epoxy part should also be identified and its feasibility established. The feasibility study should be completed at the end of the Phase I base as the down select will be made before the Phase I option is exercised. PHASE II: Using the results from Phase I, develop repair kits. Identify a control surface and an access panel. With TPOC input design and create damage on the parts. Repair the damage using the Vitrimer patches. Examine the quality of the patches through non-destructive inspection (NDI). Determine the strength of the patches through testing. At this point NAVAIR depots are expected to be involved to inform the team of the needs for repairs. Using this information as well as results from the program, design and produce prototype repair kits and demonstrate it at a Navy depot. PHASE III DUAL USE APPLICATIONS: The primary transition goal is NAVAIR depots. While interest is from PEO(A) the solution applies to all aircraft with composites. In addition to repairs, vitrimer resins have great potential in manufacturing complex production parts. In addition to the aviation industry there is also interest in vitrimers by the automotive industry, urban mobility industry, and high performance sport industry. Vitrimer composites are environmentally friendly and recyclable. Thus it has great potential as environmentally benign replacements for thermoset composite parts. REFERENCES: 1. Sloan, Jeff. Vitrimers: The reprocessable thermoset. CompositesWorld, September 28, 2020. https://www.compositesworld.com/articles/vitrimers-the-reprocessable-thermoset 2. Gardiner, Ginger. Reprocessable, repairable and recyclable epoxy resins for composites. CompositesWorld, May 24,2021. https://www.compositesworld.com/articles/reprocessable-repairable-and-recyclable-epoxy-resins-for-composites. 3. Yang, Yang; Xu, Yanshuang; Ji, Yan and Wei, Yen. "Functional Epoxy Vitrimers and Composites." Progress in Materials Science, Vol. 120, 2021/07/01: 100710. . https://www.sciencedirect.com/science/article/pii/S0079642520300748 4. Chen, Mao; Zhou, Lin; Chen, Zhongtao; Zhang, Yinyu; Xiao, Peishang; Yu, Shujun; Wu, Yeping and Zhao, Xiuli. "Multi-Functional Epoxy Vitrimers: Controllable Dynamic Properties, Multiple-Stimuli Response, Crack-Healing and Fracture-Welding." Composites Science and Technology, 221, 2022/04/12: 109364. . https://www.sciencedirect.com/science/article/pii/S0266353822001063 KEYWORDS: Vitrimer; Composite Repair; Wet Patch Layup; contested environment; depot repair; kits; recyclable