Qualification of Laser Peening on Fatigue and Fracture Critical 7085 Aluminum Structure

Aircraft structural designs have been forced to develop innovative solutions to enable survivability within the advanced battlefield of the 21st century; a key example is the unitization of structural elements. The development of more advanced metal alloying, forging processes and machining methods have enabled previously built-up structural designs to be replaced by fewer parts, less fasteners, reduced weight, and more internal carrying capacity for fuel and munitions. This paradigm of consolidated structure enables designs that save weight by reducing the number of and complexity of fastened joints, while also providing the flexibility to design more complex geometries. However, these advancements have made repairing complex unitized structural members challenging; non­ removable structures can't be replaced, and geometric requirements may preclude reinforcement by sistering. This presentation describes the qualification methodology for the application of Laser Peening (LP) to extend the service life of critical structural bulkheads on a modern fighter aircraft. These bulkheads form the major load carrying backbone of the aircraft and failure of any one of them would be catastrophic to the structural integrity of the aircraft. Thus, the presented qualification methodology ensured that the application of LP would enable the aircraft to meet its fatigue and crack growth requirements through the collective application of finite element analysis, crack growth modeling, residual stress analysis, and mechanical testing.