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

Aircraft wing skins contain thousands of fastener holes, which can act as crack initiation sites for structures under severe fatigue conditions. Major cracks have developed around aircraft fastener holes, which can propagate into larger cracks and possible result in catastrophic failure. Compressive residual stresses have been shown to improve fatigue performance for a variety of applications. Current methods of inducing compressive residual stresses in the fastener holes, using cold expansion, do not completely retard the formation and growth of cracks at the entry surface of the holes, since stresses there are lower than at the middle and exit. Gatekey Engineering, Inc., proposes to develop and demonstrate the feasibility of using Electromagnetic Pulse (EM/P) expansion processing to provide deep compressive residual stresses at the entry surface of the hole.