Haynes 230 High Temperature Thermo-Mechanical Fatigue Constitutive Model Development

Abstract

Service temperatures of propulsion turbine engine combustor components can be as high as 1,800 °F. This induces a thermo-mechanical fatigue (TMF) loading which, as a result of dwell periods and cyclic loadings, eventually leads to failure of the components via creep-fatigue processes. A large set of isothermal and anisothermal experiments have been carried out on Haynes 230, in an effort to understand its high temperature fatigue constitutive response. Isothermal experiments at different loading strain rates show that the material can be considered to be rate-independent below and at 1,400 °F. However, isothermal strain hold experiments show stress relaxations below and at 1,400 °F. The out-of-phase strain-controlled TMF experiments show a mean stress response. A Chaboche based viscoplastic constitutive model with various features is under development with the final objective of predicting the strains in an actual combustor liner in service through finite element simulation for fatigue lifing. Temperature rate terms have been found to improve hysteresis loop shape simulations and static recovery terms are essential in modeling stress relaxation at temperatures where the behavior is overall rate-independent. It is anticipated that the new modeling feature of mean stress evolution will model the experimentally observed thermo-mechanical mean stress evolution.