Non-Local Cyclic Life Prediction for Gas Turbine Components With Sharply Notched Geometries

The safe and efficient operation of modern heavy duty gas turbines requires a reliable prediction of fatigue behaviour of turbine components. Fatigue damage is located in areas where cyclic stress and strain amplitudes are highest. Thus, geometrical notches associated with stress/strain concentrations and stress/strain gradients appear to be the most important sites for fatigue crack initiation. The paper addresses a non-local concept for fatigue life prediction of notched components. In contrary to various local approaches in the field, the proposed method explicitly accounts for stress and strain gradients associated with notches, cooling holes, fillets and other design features with stress raising effect. As a result, empirical analytical expressions for considering either strain or stress gradients on cyclic life prediction are obtained. The method has been developed from cyclic test data on smooth and notched specimens made of a ferritic 1.5CrNiMo rotor steel. The obtained analytical formulations have then been applied to test data on the Nickel base superalloy MAR-M247 CC showing a good agreement between prediction and measurement. Moreover, the proposed non-local lifing concept has been validated by component tests on turbine blade firtrees. The predicted cycles to failure correlates well to the experimental results showing the applicability of the proposed method to complex engineering designs.