Bolt Hole Corrosion and Fatigue Damage Repair in Hybrid Vertical Lift Structure

Cold expansion has been successfully used in aerospace structures, including vertical lift airframes to repair and prevent fatigue damage for more than 50 years. PartWorks is innovating the cold expansion process, parts and tooling for use in repairing corroded fastener holes (U.S. Patent 11,255,371). PartWorks is participating in a two phase development and demonstration program, first for the US Navy (Office of Naval Research/ONR) starting in 2017, and more recently for the United States Air Force (Air Force Research Lab/AFRL) for repairs to bolt holes on aerospace structures with metal/carbon-fiber composite skins. These locations in aerospace structures for vertical lift or fixed wing have demonstrated greater levels of corrosion when compared to all-metal structural skin due to galvanic corrosion between metal and carbon fiber composites. Existing repair methods for these metal/carbon fiber composite skin bolt hole/fastener sites often involve extensive removal of corrosion, non-standard or oversized holes, and extensive modeling/validation to prove repair effectiveness. Existing repairs can also lead to premature structural component replacement. This project is evaluating a new repair method that uses cold expansion with thin wall bushings and/or a rivetless nut plate (RNP) to restore fatigue life to the metal bolt hole if damage is missed or potentially without having to remove all the damage/corrosion.