In the aircraft industry residual stresses have been utilized for long time to increase the fatigue performance of structural elements by cold hole expansion and shot peening. Next to these intentional stresses, residual stresses are also present in the structure as a result of the manufacturing process and aircraft assembly. It is well-known that tensile residual stresses decrease fatigue life, while on the other hand compressive residual stresses increase fatigue life. Despite of this, the aerospace industry still does not give credit to residual stress as a design parameter, mainly because of the poor correlation between experimental and predicted crack growth rates. It is believed that this is mainly due to confounding factors like heat affected
zones in welding, two-dimensional crack fronts, sub-surface inititation, multiple cracking and an inaccurate residual stress estimation in the experiments.