CONSTITUTIVE MODEL BASED EFFICIENT CREEP-FATIGUE DAMAGE COMPUTATION TECHNIQUE FOR STEAM TURBINE ROTORS TO ENHANCE FLEXIBLE OPERATIONAL CAPABILITIES

In the new era of renewable energy, flexible operation of conventional power plants is inevitable, causing high creepfatigue life consumption. Conventional life assessment methods are deemed to be conservative to address the current requirements. The use of unified constitutive models for the analysis of damage evolution in steam turbine rotors in the past decade has shown promising results and closely relate to experimental data. However, identification of large number of material constants and high computational efforts hinder the widespread use of such models. In this paper, the latter is addressed using a novel representative input cycle (RIC) concept together with the non-iterative asymptotic numerical method (ANM). Various start-up shutdown sequences of a typical steam turbine rotor are studied using a unified constitutive model based on Chaboche's kinematic hardening including the damage parameter, Chaboche-Rousselier's isotropic hardening model including the damage parameter, Norton's viscoplastic flow model, Lemaitre's damage potential function and Kachanov-Rabotnov's creep damage law. First, a conventional FEM technique is used and then the proposed RIC method is used to study the evolution of inelastic variables. The reduction in computational efforts and the compromise in accuracy using the proposed method is studied.