Power-exponent function model for low-cycle fatigue life prediction and its applications – Part II: Life prediction of turbine blades under creep–fatigue interaction

Abstract

This paper is concerned with the applications of the proposed models, namely the modified linear damage summation (MLDS) method and the modified strain range partitioning (MSRP) method described in Part I of the series papers, to life prediction of turbine blades under creep–fatigue interaction. To begin with, a detailed FEM analysis is conducted considering peak loading of thermal load, centrifugal force and airflow force to determine life assessment positions. Secondly, according to the blades rig testing load, a stress–strain response analysis is performed for pure low-cycle fatigue (LCF) and creep–fatigue interaction, in which steady-state temperature field, plastic kinematic hardening and contact between the blade body and hoop segment are taken into consideration to achieve accordance with practical conditions. Finally, based on FEM simulation results, the life of turbine blades is predicted using the five different models for creep–fatigue loading. A minimum safe and conservative life of 1293 h is given by the MLDS method based on power-exponent function model. The predicted lives by the MLDS and MSRP methods show reasonable agreement with the rig testing life, which further illustrates the validity of power-exponent function model and its applications.