Non-Contact Process to Enhance the Fatigue Life of Aluminum Cold Worked Fastener Holes

Fatigue crack on the aircraft wing skins after extended service is a significant reliability issue for structural integrity. Fatigue cracks originating from fastener hole surfaces can grow eventually leading to catastrophic failure of the structure. Inspecting the holes and repairing cracks are expensive and time consuming with significant downtime of the aircraft. Cold expansion can be applied to the fastener hole to introduce a compressive stress to extend the fatigue life of the structure, but hole cold expansion does not give even compressive stress through the fastener hole sections. Luna Innovations Incorporated proposes a fiber optics based laser peening system to treat fastener holes as small as 0.18 inch. With fiber optics probe design, double shot laser coupling and liquid phase laser energy absorbing coating, the laser peening fiber optics system will be able to deliver sufficient compressive stress to the entry section of the fastener hole at higher peening rate. The fatigue life of the structural component will thus be extended with reduced maintenance cost and risk of structural failure.