A pathway for certifying engineered residual stress for aircraft sustainment and life extension

Aircraft Structure and Systems require a specific number of fight hours to achieve their design lifetime. Significant increases in the cost of manufacture coupled with reduced budgets for purchase of new aircraft have created a need for processes that extend the service life beyond design limits in both commercial and military aircraft. Deep compressive residual stresses developed by Laser peening have shown the capability to extend fatigue lifetime 200 to 1000% providing increased fatigue strength, damage tolerance, resistance to foreign object damage, fretting, and stress corrosion failures. This large fatigue enhancement makes up for the cost of processing by increasing system availability, reducing cost of part replacements and decreasing the cost and time for needed inspections.

Credit can be taken for life extension generated by laser peening because each laser spot placement is precisely robotically controlled and a computer record of that energy is sampled and recorded. Testing of materials including; aluminum, titanium, high strength steels, stainless steels and magnesium show that laser peening can be applied to most aircraft materials. Parts are currently being processed when new, during overhaul/repair or on the aircraft during routine maintenance. Laser peening is currently being applied to aircraft components including; engine disks, blades, actuators, aircraft structure, arresting hooks and forming of wing skins. The process can be applied on location or the parts shipped to a facility providing this service.

Finite Element Modeling now incorporates the laser generated stress and strain into the component load stresses allowing the design engineer to assess the fatigue benefit via, for example, a Goodman diagram before costly fatigue testing thereby significantly reducing trial and error iterations of process parameters. Fatigue test coupons incorporating the same geometric load paths, materials, heat treat and coatings are used for qualification. Examples and test results of representative parts will be shown.