Multiaxial fatigue life prediction of a high temperature steam turbine rotor using a critical plane approach (original) (raw)
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Multiaxial high-cycle fatigue criteria and life prediction: Application to gas turbine blade
International Journal of Fatigue, 2016
A recent work conducted by the authors [Maktouf, W., Saï, K., 2015. An investigation of premature fatigue failures of gas turbine blade. Engineering Failure Analysis, 47, 89-101.] demonstrated that the root cause of the premature blade failure was caused by high-cycle fatigue (HCF) mechanism initiated at a localized carbon-rich area inducing grain boundary brittleness. The blade was subject to multiaxial cyclic loadings during its service life and any attempt to assess component fatigue strength leads to the question of choosing an appropriate fatigue design criterion. In this paper several multiaxial fatigue models are applied as post-processing step of the Finite Element Analysis (FEA) output results and the estimated fatigue lifetimes were assessed under different loading conditions. The material fatigue parameters, required as an input to the selected fatigue models were determined through a series of bending and torsion tests on specimens made of aged Inconel 718. A numerical post-processing algorithm was developed for Fatemi-Socie fatigue criterion and included as additional post-computation model in the used computer aided fatigue damage evaluation tool. The authors point out that the majority of the multiaxial fatigue studies available in the literature are conducted mainly for correlating the experimental laboratory results on specimens while they have been used in the frame of this study to investigate their application to an industrial case.
Acta Mechanica et Automatica, 2018
The paper analyses the possibility of using analytical methods of notch stress-strain correction in low-cycle fatigue life predictions of steam turbine rotors operating under non-isothermal conditions. The assessment was performed by comparing strain amplitudes calculated using the Neuber and Glinka-Molski methods and those predicted by the finite element analysis (FEA) employing elastic-plastic material model. The results of investigations reveal that the Neuber method provides an upper bound limit, while the Glinka-Molski method results in a lower bound limit of strain amplitude. In the case of rotor heat grooves, both methods provide equally accurate results of notch strain amplitude and are suited to estimating lower and upper bound limits of low-cycle fatigue life under non-isothermal conditions.
Thermo-Mechanical Fatigue Life Assessment of a Gas Turbine Rotor Through Reliability Approach
Journal of Failure Analysis and Prevention, 2018
Turbine rotor is a critical and life-limiting component in gas turbine engines. The thermo-mechanical fatigue (TMF) life of a turbine rotor was studied using reliability method. The fatigue life was estimated using (a) Marrow's model and (b) Smith-Watson-Topper model. The creep life was estimated based on Larson Miller equations and finite element analysis. The cumulative fatigue-creep damage was estimated, and the turbine rotor TMF life was estimated against the data variation. The reliability approach takes care of material property variations, load variations and geometrical variations. These variations bring out the scatter in component stress-strain and further into life. The scattered life spells out the component reliability. The TMF life was modeled as Weibull distribution, and the reliability was estimated. The component was tested for structural integrity through hot cyclic spin test, and the results were compared with the predictions. The blade growth and strain estimations using Marrow and SWT-creep methods were found in good agreement with the test values.
Thermo-mechanical fatigue prediction of a steam turbine shaft
MATEC Web of Conferences
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.
International Journal of Engineering Research and Technology (IJERT), 2013
https://www.ijert.org/low-cycle-thermal-fatigue-damage-in-steam-turbine-rotor-analytical-evaluationof-remaining-life-a-case-study https://www.ijert.org/research/low-cycle-thermal-fatigue-damage-in-steam-turbine-rotor-analytical-evaluationof-remaining-life-a-case-study-IJERTV2IS2514.pdf This paper discusses about a case study for analytical evaluation of low cycle thermal fatigue damage of a high pressure (HP) rotor of 210 MW steam turbine during transient. The thermal strain also has been evaluated analytically.The assessment of the damage has been checked by analytical method namely cyclic life expenditure (CLE), which essentially utilizes the proprietary information of the turbine manufacturer whereas the former method utilizes the accessible published information. In the absence of actual material properties data of the rotor, certain permissible practical assumptions have been made in the study here. The analytical method may help in quick assessment of low cycle fatigue (LCF) damage of a steam turbine rotor during transient.
Procedia Structural Integrity, 2018
During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.
Thermo-Mechanical Fatigue Analysis of a Steam Turbine Shaft
Acta Polytechnica CTU Proceedings
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.
Multiaxial Fatigue Criterions Applied to Mechanical Components
In many practical situations, mechanical components are subjected to multiaxial loading and the required design lifetime often exceeds 10 8 cycles. For example, the expected lifetime of engine components, railroad wheels, crankshafts, turbine blades, etc. is more than 10 9 cycles. The traditional fatigue criterions assumed a hyperbolic relationship between stress and fatigue life, but experimental results in steels show that the fatigue fracture can occur beyond 10 7 cycles. This means that for very high number of cycles the fatigue limit does not an asymptotic behaviour and the concept of infinite fatigue life is not correct. So, the fatigue in metal components with design lifetimes greater than 10 7 cycles is an interesting topic for the development of advanced technologies. Taking into account that experimental fatigue tests are very expensive and time-consuming, the development of numerical fatigue models capable of predicting the durability of components, is a key task to carry out mechanical components design in shorter times. Multiaxial fatigue criterions can be classified in the following way: 1) Empirical, 2) Stress Invariants, 3) Critical Plane, 4) Strain Energy, 5) Combined Energy/Critical Plane and 6) Mesoscopic. In this paper, we present results from numerical models using the finite element method (FEM) analyzing mechanical components subjected to high number of impact cycles with an invariant criterion.
MATEC Web of Conferences
Corrosion fatigue fractures initiating from corrosion pits are one of the most serious problem during service of rotating blades of the low-pressure parts of steam turbines. A methodology for fatigue failure prediction, originally based on the knowledge obtained by EPRI (Electric Power Research Institute), using corrosion pits parameters assessment and local stresses calculation was adapted to the conditions of ČEZ a.s. power stations. This contribution deals with the evaluation of the corrosion state of blades of three low pressure rotors after long service. Measurement was done in power stations equipped with turbines of power 200 MW and 110 MW respectively. Possibilities and uncertainties (influence of filling of pits with oxides, cyclic stress calculations, and the selection of the geometric factor Y) and their elimination are discussed.