Fatigue life prediction of complex 2D components under mixed-mode variable amplitude loading

Accurate residual fatigue life predictions under variable amplitude (VA) loading are essential to maximize the time between the required inspections in defect-tolerant structures. However, this is not a trivial task for real structural components, in which cracks may change direction as they grow due to mixed-mode loading. Such curved crack paths can be predicted using finite element (FE) techniques, but this approach is not computationally efficient to predict the residual life, because it would require timeconsuming remeshing of the entire structure after each rain-flow counted load event under VA loading. In this work, a two-phase methodology that is both precise and cost-effective is applied to solve this problem. First, the fatigue crack path and stress intensity factors KI and KII are calculated in a specialized (global) FE program using fixed crack increments, requiring only relatively few remeshing steps. Then, an analytical expression is fitted to the calculated KI(a) values, where a is the length along the crack path, and exported to a companion fatigue design program to predict the crack propagation life by the local approach, considering load interaction effects such as crack retardation or arrest after overloads. This two-phase methodology is experimentally validated by fatigue tests on compact tension specimens, modified with holes positioned to attract or to deflect the cracks.  2003 Elsevier Ltd. All rights reserved.