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

Fatigue crack growth analysis of the low-pressure rotor of the steam turbine

Tento příspěvek shrnuje aplikovaný numericko-analytický přístup k predikci směru a rychlosti šíření trhlin v potenciálně kritických lokalitách hřídele nízkotlaké části parní turbíny. Primárním cílem bylo poskytnout hodnotící hledisko pro posouzení trojice kandidátních materiálů pro konstrukci hřídele v daných provozních podmínkách a s ohledem na předpokládaný charakter šíření trhlin. Výsledkem jsou predikované růstové křivky modelových trhlin, resp. diagramy mapující charakter šíření trhlin v podmínkách kombinovaného namáhání drážky závěsu lopatky turbíny.This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Grant Agreement 764545– TURBO-REFLEX.This paper summarizes the applied numerical-analytical approach for predicting the fatigue crack growth rate and direction of propagation in potentially critical localities of the shaft of the low-pressure part of the steam turbine. The primary objective was to develop a means of evaluation of a pair of candidate materials applicable to shaft design under given operating conditions and with respect to the expected mechanism of crack propagation. As a main result, predicted fatigue crack growth curves of model cracks and diagrams mapping the nature of crack propagation in the conditions of combined loading of the turbine blade groove were obtained

Deep levels in homoepitaxial boron-doped diamond films studied by capacitance transient spectroscopies

International audienceDeep level transient spectroscopies (DLTS) applied to Schottky junctions made on homoepitaxial boron-doped diamond films show the existence of two traps. A deep acceptor, negatively charged and strongly attractive for holes, 1.57 eV above the valence band edge displays the characteristic features of a complex defect due to interacting centers and impurities, also displaying some evolutions after thermal cycles, possibly due to hydrogen effusion or diffusion. It is tentatively ascribed to association of a boron atom, a vacancy and several hydrogen atoms. A deep donor, 1.13 eV above the valence band edge, able to compensate the boron acceptors, is attributed to a defect correlated with dislocations. It could be due to the positively charged carbon vacancy. These conclusions are drawn from the Fourier transform-DLTS results coupled with isothermal time domain algorithms allowing the discrimination of multiple emission rates with high resolution

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

Sociální služba osobní asistence a problémové oblasti z pohledu informační a metodické podpory při poskytování služby v době pandemie Covid-19

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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

Weak localization in ultrananocrystalline diamond

In this letter we present results of magnetotransport measurements, carried out on heavily nitrogen-doped ultrananocrystalline diamond films, prepared by plasma-enhanced chemical vapor deposition. This material having at room temperature appreciably high electric conductivity ( ∼ 4200 S m−1) revealed surprisingly at Kelvin temperatures a giant negative magnetoresistance reaching up to 22% at 1.28 K and at 8 T. The analysis of experimental data has borne evidence of the fact that the transport in this subsystem has a character of low-dimensional disordered metal and it is controlled by quantum interference effects of electrons resulting in their weak localization

Diamond/Porous Titanium Nitride Electrodes With Superior Electrochemical Performance for Neural Interfacing

Robust devices for chronic neural stimulation demand electrode materials which exhibit high charge injection (Qinj) capacity and long-term stability. Boron-doped diamond (BDD) electrodes have shown promise for neural stimulation applications, but their practical applications remain limited due to the poor charge transfer capability of diamond. In this work, we present an attractive approach to produce BDD electrodes with exceptionally high surface area using porous titanium nitride (TiN) as interlayer template. The TiN deposition parameters were systematically varied to fabricate a range of porous electrodes, which were subsequently coated by a BDD thin-film. The electrodes were investigated by surface analysis methods and electrochemical techniques before and after BDD deposition. Cyclic voltammetry (CV) measurements showed a wide potential window in saline solution (between −1.3 and 1.2 V vs. Ag/AgCl). Electrodes with the highest thickness and porosity exhibited the lowest impedance magnitude and a charge storage capacity (CSC) of 253 mC/cm2, which largely exceeds the values previously reported for porous BDD electrodes. Electrodes with relatively thinner and less porous coatings displayed the highest pulsing capacitances (Cpulse), which would be more favorable for stimulation applications. Although BDD/TiN electrodes displayed a higher impedance magnitude and a lower Cpulse as compared to the bare TiN electrodes, the wider potential window likely allows for higher Qinj without reaching unsafe potentials. The remarkable reduction in the impedance and improvement in the charge transfer capacity, together with the known properties of BDD films, makes this type of coating as an ideal candidate for development of reliable devices for chronic neural interfacing