Modelling of the transition from mode I to crystallographic crack growth in a single crystal gas turbine blade alloy under service-like loading conditions

In fatigue life prediction of single crystal gas turbine blades, the risk of rapid crystallographic crack growth along the close-packed planes poses a large uncertainty. A criterion is proposed to predict the transition from mode I to crystallographic crack growth, which is necessary for reliable prediction of the number of cycles from crack initiation to the onset of crystallographic crack growth. The proposed criterion is calibrated against tests performed under a wide range of conditions representative for a gas turbine blade, including isothermal fatigue crack growth tests and thermomechanical fatigue crack growth tests, some including hold times and pre-test aging.
Funding agencies: The work has been supported financially by Siemens Energy AB in Finspång, Sweden and the Swedish Energy Agency, via the Research Consortium of Materials Technology for Thermal Energy Processes, Grant No. KME-702.