Variable amplitude fatigue of autofrettaged diesel injection parts

Experimental and analytical investigations of constant and variable amplitude fatigue life of not autofrettaged and autofrettaged components have been performed. In variable amplitude loading the new standardised COmmonRAilLoad sequence CORALhas been used as well as twoleveltests with small cycles at high mean stresses interrupted by large cycles for the evaluation of load sequence effects. The results of the two level tests show that small cycles with amplitudes far below the fatigue limit cause fatigue damage. Life calculations have been performed according to the nominal stress approach with SNcurves and improved Miner’s Rule, linearelastic fracture mechanics with 3Dweight functions,elasticplastic fracture mechanics applying an extended strip yieldmodel, and explicit 3DFEsimulation of fatigue crack growth with predefined crack fronts.All approaches are appropriate for predicting realistic variable amplitude lives. From a practical point of view the explicit 3DFEsimulation of fatigue crack growth is too timeconsuming. However, such simulations show that the approaches based on linearelastic fracture mechanics and elasticplastic fracture mechanics with extended strip yieldmodel capture the essential physics of fatigue crack growth in a realistic way.