A lifing method based on R5 and viscoplasticity modelling and its application to turbine rotor under thermomechanical loading

An integrated life assessment procedure for structures operating under thermomechanical loading has beendeveloped. The methodology uses a viscoplasticity based framework combined with the R5 life assessment code. Theviscoplastic constitutive model used for the stress-strain analysis is derived from the Chaboche-Lemaitre formulationthat allows to directly obtain the required parameters for the R5 assessment as stress relaxation per cycle and theelastic follow-up factor. The R5 procedure is therefore significantly simplified. The proposed life assessment procedureis demonstrated on a martensitic steel (FV566) industrial gas turbine rotor under a typical start up – shut downoperation. The effect of creep-fatigue interaction at different locations within the rotor structure is assessed and theremaining life at each location is calculated. A sensitivity study is performed at half load, which shows an increase inlifetime of the rotor