EQUIVALENT CONSTANT AMPLITUDE CONCEPTS EXAMINED UNDER FATIGUE CRACK PROPAGATION BY BLOCK LOADING

— Fatigue crack growth behaviour under block loading sequences has been studied on the aluminium alloy 2024 T351, using four different equivalent constant amplitude concepts. The root mean squared method gives acceptable results only for relatively long blocks. The equivalent method based on the Paris law (modified to take into account crack closure) gives good predictions for the observed growth rates as does Elbers' method. Finally, a new method based on energy considerations gives excellent results for the studied test conditions.