Incremental fatigue damage model : Application to plane problems with non-proportional loading

Modern airframe aluminum structures are increasingly manufactured in large and complex integral parts. Suchparts are often exposed to in–plane, non–proportional loading and contain stress–raisers with complex geometry. Conventional methods, based on the stress concentration factor and cycle counting, are unsuitable forassessment of this type of problem. We present a fatigue damage model, based on the concept of movingendurance surface and incremental damage evolution. The fatigue damage is entirely dependent on the localstress history and the notch effect is accounted for by introduction of the relative stress gradient. Also, wepresent an automated and efficient implementation of the model, for the purpose of computing fatigue damageat stress raisers in plane problems with non–proportional loading. We demonstrate the implementation by anexample of a fatigue calculation in an aircraft frame.