Differences in the response to in-phase and out-of-phase multiaxial high-cycle fatigue loading

This paper discusses the phase shift effect occurring between two and more load channels of multiaxially loaded specimens. The discussion concludes that there is an extreme shortage of good experimental data that would prove the existence and the trend of the phase shift effect in the high-cycle fatigue region. It is no wonder that there are so many fatigue strength estimation criteria that use quite different computational concepts, because the response to the phase shift effect in the experimental base is often hidden in a conglomeration of other interacting effects. The paper presents results of a sensitivity study that compares the fatigue strength estimation results for various such criteria for the same stress amplitudes, but for different phase shifts between the push-pull and torsion load channels. These results show that, with the exception of criteria, that assume a zero phase shift effect, the phase shift affects the results of each studied fatigue strength estimation criterion in a different way. If well-organized experiments were available, experiments corresponding to the described comparison between in-phase and out-of-phase loading would show the right trends, and the optimum criterion could be selected. A proposal for such an experimental setup is provided in the paper

Thermomechanics fatigue damage methodlogy of the turbine rotor

Příspěvek se zabývá metodikou výpočtu životnosti a stanovením kritických míst rotoru turbíny při zvýšené četnosti teplých i studených startů a následně postupy vyhodnocování únavového poškozování s využitím teorií kombinace nízkocyklové (vysokocyklové) únavy a creepu, zejména potom Sehitoglu modelem a modelem dle Nagodeho. Popisuje potřebné materiálové parametry a schéma programových skriptů a postupu numerických simulací.This paper describes a fatigue life methodology and determination of critical points of the turbine rotor by increased frequency of both hot and cold operational starts, followed by methods of evaluation of fatigue damage using the combination of low cycle (fatigue) and creep theory, especially the Sehitoglu and the Nagode models. It describes the necessary material parameters and schema of the program scripts and the procedure of numerical simulations

THERMO-MECHANICAL FATIGUE ANALYSIS OF A STEAM TURBINE SHAFT

Increasing demands on the flexibility of steam turbines due to the use of renewable energy sources substantially alters the fatigue strength requirements of components of these devices. Rapid start-ups as well as the increased number of the load cycles applied to the turbines must be handled by design methodologies. The goal of the work presented in this paper was to provide a computational framework applicable to the thermo-mechanical fatigue (TMF) prediction of steam turbine shafts. The so-called Damage Operator Approach by Nagode et al. has been implemented to the software codes and applied to fatigue analysis of the thermo-mechanical material response computed numerically by the finite element analysis. Experimental program conducted in order to identify the material thermo-mechanical behavior and to verify numerical simulations is introduced in the paper. Some results of TMF prediction of a sample steam turbine shaft are shown

Thermomechanics fatigue damage methodlogy of the turbine rotor

Příspěvek se zabývá metodikou výpočtu životnosti a stanovením kritických míst rotoru turbíny při zvýšené četnosti teplých i studených startů a následně postupy vyhodnocování únavového poškozování s využitím teorií kombinace nízkocyklové (vysokocyklové) únavy a creepu, zejména potom Sehitoglu modelem a modelem dle Nagodeho. Popisuje potřebné materiálové parametry a schéma programových skriptů a postupu numerických simulací.This paper describes a fatigue life methodology and determination of critical points of the turbine rotor by increased frequency of both hot and cold operational starts, followed by methods of evaluation of fatigue damage using the combination of low cycle (fatigue) and creep theory, especially the Sehitoglu and the Nagode models. It describes the necessary material parameters and schema of the program scripts and the procedure of numerical simulations

Thermo-mechanical fatigue prediction of a steam turbine shaft

The increasing demands on the flexibility of steam turbines due to the use of renewable energy sources substantially alters the fatigue strength requirements of components of these devices. This paper presents Thermo-Mechanical Fatigue (TMF) design calculations for the steam turbine shaft. The steam turbine shaft is exposed to complex thermo-mechanical loading conditions during the operating cycle of the turbine. An elastic-plastic structural Finite Element Analysis (FEA) of the turbine shaft is performed for the turbine operating cycle on the basis of calculated temperature fields obtained in a previous transient thermal FEA. The temperature dependent material parameters, which are used in the elastic-plastic FEA, are obtained from the uniaxial tests. Consequently, the TMF is predicted for the steam turbine shaft. Several fatigue criteria are used for the identifications of the critical domain and for the TMF damage assessment of the turbine shaft

Thermo-mechanical fatigue prediction of a steam turbine shaft

The increasing demands on the flexibility of steam turbines due to the use of renewable energy sources substantially alters the fatigue strength requirements of components of these devices. This paper presents Thermo-Mechanical Fatigue (TMF) design calculations for the steam turbine shaft. The steam turbine shaft is exposed to complex thermo-mechanical loading conditions during the operating cycle of the turbine. An elastic-plastic structural Finite Element Analysis (FEA) of the turbine shaft is performed for the turbine operating cycle on the basis of calculated temperature fields obtained in a previous transient thermal FEA. The temperature dependent material parameters, which are used in the elastic-plastic FEA, are obtained from the uniaxial tests. Consequently, the TMF is predicted for the steam turbine shaft. Several fatigue criteria are used for the identifications of the critical domain and for the TMF damage assessment of the turbine shaft