Creep and Thermomechanical Fatigue Modelling of Single Crystal Superalloy Turbine Blades

Gas turbine engine rotor blades are being manufactured increasingly from nickel-based single crystal superalloys. Intended for use in the hottest sections of the turbine, these alloys are capable of providing large increases in component endurance and reliability, as well as engine performance due to increased turbine entry temperature levels. To ensure full utilisation and calculation of safe component life times, accurate modelling of the non-linear deformation suffered during typical duty cycles is needed. The Mechanical Sciences Sector at DERA, Farnborough has developed an anisotropic creep analysis and modelling capability specifically targeted at simulating the high temperature creep and thermomechanical fatigue behaviour of superalloy single crystal specimens and turbine blades under complex loading and non-isothermal conditions. The model has been incorporated into a user material subroutine (UMAT) for use with the ABAQUS finite element programme, within which the inelastic strain is considered to be a combination of the instantaneous plastic strains, time-dependent creep strains and thermal strains. A recent collaborative programme between Alstom Power (UK) and DERA has applied this model to generate predictions for the anisotropic creep and thermomechanical fatigue behaviour of a number of specimen and blade designs.