Yevgen Kostenko

Robust Methods for Creep Fatigue Analysis of Power Plant Components Under Cyclic Transient Thermal Loading

The aim of this paper is to apply robust mechanisms-based material laws to the analysis of typical high-temperature power plant components during an idealized start-up, hold time and shut-down sequence under a moderate temperature gradient. Among others a robust constitutive model is discussed, which is able to reflect inelastic deformation, hardening/recovery, softening and damage processes at high temperature. The model is applied for a creep analysis of advanced 9–12%CrMoV heat resistant steels and calibrated in particular case against experimental data for 10%CrMoV steel type. For a steam temperature profile transient heat transfer analysis of an idealized steam turbine component is performed providing the temperature field. From the subsequent structural analysis with the inelastic constitutive model local stress and strain state variations are obtained. As an outcome a multi-axial thermo-mechanical fatigue (TMF) loading loop for one or several loading cycles can be generated. They serve as input for a fatigue life assessment based on the generalized damage accumulation rule, whose results come close to reality. In addition, the accuracy of a simplified method which allows a rapid estimation of notch stresses and strains using a notch assessment rule (NAR) [1] based on Neuber approach is examined.Copyright

Power Plant Component Design Using Creep-Damage Analysis

The constitutive equation for the creep deformation rate, as well as the kinetic equations for hardening, recovery and damage processes, with a continuous functional dependence on temperature, are proposed. The material model is able to describe the primary, secondary and tertiary stages of creep behavior. The technique for the identification of parameters in the uniform model is developed on the basis of experimental creep curves for a wide range of temperatures and stresses. The parameter fitting for a creep-damage model with temperature dependence is carried out for one typical heat-resistant steel widely used in the power plant industry. Numerical results are obtained by the Finite-Element-Method for a real power plant component using the ABAQUS code and incorporated user-defined materials routines.Copyright