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

The United States Navy (USN) Office of Naval Research (ONR) needs the capability to repair contoured surfaces of carbon fiber reinforced composites (CFRCs) in forward deployed and contested environments. The typical repair uses a wet-layup patch; however, this generally results in a knockdown in strength. Therefore, the USN is seeking a robust, low-cost, easy-to-process vitrimer resin-based CFRC patch that can be deployed with the fleet to perform repairs in theater that will restore the full strength of in-service CFRCs. Several unmanned aerial systems (UASs) are in use by the USN and United States Marine Corps (USMC) such as: a) MQ-9A Reaper (USMC, PMA-266), b) MQ-4C Triton (USN, PMA-262), and 3) Small UAS Reusable Architecture (SRA) (USN/USCM, PMA-263). Vitrimer patches are a novel progression from conventional thermoset repairs. Cured vitrimers feature dynamic crosslinking above a threshold temperature (Tv). This allows for the possibility of reformable, re-curable patches for repair, even on conventional composite damage sites. Several new vitrimer chemistries have been developed that would allow for reversible crosslinking (which enables reprocessing and reshaping at temperatures above the cure temperature), but most of these formulations lack the scale or properties of conventional thermosets. The ability to have both features is highly desirable. The team will fabricate vitrimer/carbon fiber (CF) patches to effectively repair epoxy/CF composites for UASs at maintenance depots and/or in-field in forward deployed/contested environments. The vitrimer/CF patches will be fabricated by melt pressing in-house vitrimer resin into non-woven and satin weave CF preforms. Vitrimer composites can also be used as reversible adhesives. If a vitrimer adhesive becomes misaligned or delaminates during a repair due to user error, the adhesive can be reheated, debonded, and realigned correctly and rebonded. In previous work, electromagnetic heating was used to bond and debond two epoxy specimens using a vitrimer/epoxy/carbon nanotube adhesive. The adhesive lap shear strength was measured after each cycle of bonding, and even after the fifth cycle, 70% of the initial adhesive strength is retained. This demonstrates that vitrimer composites can be utilized as reusable adhesive patches.