Lifetime Of Components Research Articles

점검-정비 모형에서 열화부품의 발견확률을 고려한 시스템의 최적 점검주기

Purpose: The determination of the optimal inspection interval of a system is a critical factor that can influence its maintenance. Frequent inspections yield shorter inspection intervals and higher inspection costs compared with infrequent inspections, which lead to an increase in the total maintenance cost due to the frequent occurrence of failures. The objective of this study is to determine the optimal inspection interval, which minimizes the total expected cost until the system is overhauled.BRMethods: We developed an inspection - maintenance cost model by considering the unit inspection cost, the cost for preventive maintenance, and the cost for corrective maintenance as well as the cost and quantity of a component, the distribution of the lifetime of components, and the probability of finding fault or failure during inspections.BRResults: We propose a novel method for determining the optimal inspection interval, which minimizes the total expected cost. The proposed method can be applied to systems consisting of one or more types of components. The data, which is derived from the case study that is documented in the previous research [13], are utilized to illustrate that the proposed method is effective for determining the optimal inspection interval and for conducting sensitivity analysis. Finally, we apply the proposed method to determine the optimal inspection interval pertaining to a component of auxiliary power that is built into railway trains. Consequently, we observed that a relationship exists between the reduction in the cost of operating the system and the current inspection interval.BRConclusions: The proposed method can be effective for other repairable systems, which undergo inspection, preventive maintenance, and corrective maintenance.

A reliability evaluation method for phased‐mission system considering multi‐mechanism coupling within phases

AbstractDue to the difference of environmental stress and system configuration, as well as the coupling between phases, the phased‐mission system (PMS) has significant disparity in the failure modes and mechanisms of components in different phases. From the perspective of failure mechanism, an initial independent one will affect or be affected by other failure mechanisms during a task, and eventually leads to the failure of system. Therefore, the coupling of failure mechanisms in PMS is considered in this paper, and the recursive quantitative analysis of coupling from failure mechanism level to system level and phase level are accomplished by means of the basic rules of reliability physics. Furthermore, taking a core circuit from an aircraft electronic system as an example, the reliability modeling and analysis are performed. The results show that after considering the coupling relationship between failure mechanisms within each phase, the reliability and lifetime of components are reduced compared with the mechanism‐ independence situation, however, the cumulative failure probability of the system is increased. It reveals that it is very important to involve the coupling relationship between failure mechanisms in the reliability analysis of PMS, which can improve the accuracy of the prediction.

Broad intrinsic luminescence properties in Nb4TeO12 mixed-metal niobate tellurite

Mixed-metal oxides composed of Nb5+(d0) and Te4+(p-) cations generally exhibit excellent optoelectronic properties due to the stereoactive lone pair of electrons in the structure. In this work, a mixed-metal niobate tellurite Nb4TeO12 was prepared using solid state reaction method. The polycrystalline samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), optical absorption, photoluminescence (PL) and dynamic properties. This sample shows characteristic indirect electronic transitions with an interband energy of 3.01 eV. The bottom of conduction band and the top of valence band are +0.37 eV and +3.38 eV, respectively. Using a Nd:YAG pulsed laser as the excitation light source, the intrinsic luminescence of Nb4TeO12 was investigated over a wide temperature range of T = 10–300 K. The broad band emission peaking at 513 nm corresponds to the self-activating luminescence of the niobate octahedral group [NbO6]7−. The luminescence decay curve did not depend on the laser excitation energy, and it showed a non-exponential characteristic with two decay lifetime components. The experiments also preliminarily studied the performance of the luminescence application of Nb4TeO12.

High temperature thermographic phosphors YAG:Tm;Li and YAG:Dy in reduced oxygen environments

Phosphor thermometry for surface temperature measurements has become an established remote thermometry technique. However, measuring at temperatures above 1700 K is still challenging because of the weak phosphorescence and intense background from black-body radiation, leading to low signal-to-noise ratios. Therefore, lifetime-based phosphor thermometry with YAG:Tm;Li and YAG:Dy for high-temperature applications were investigated in this study with the aim of improving the precision of high-temperature measurements. The phosphors were coated on an alumina-oxide disc, which was placed in a temperature-controlled oven that exposed the phosphors to temperatures of up to 1930 K. The emission spectra and temporal decay of the luminescence were recorded for the investigated phosphors including their sensitivity to oxygen concentration in the gas environment. Knowledge of oxygen environment sensitivities for measurements of reduced oxygen concentrations at high temperatures, such as in combustion, is of great importance to increase confidence in the measurement. The results suggest that performing a mono-exponential decay time fit in a region of the decay curve that is dominated by a single lifetime component reduces the sensitivity to changes in the gas oxygen concentration for YAG:Tm;Li. Moreover, YAG:Tm;Li performs better than YAG:Dy in terms of signal-to-noise ratio (SNR), with a peak signal value and SNR almost an order of magnitude higher. With an appropriate decay curve fitting procedure, the effects of oxygen quenching can be minimized, such that the measurement error due to oxygen quenching is within the measurement precision for both phosphors.

S3P– Innovative Surface Treatment to Increase the Wear Resistance of Stainless Steel Components*

Abstract Austenitic and duplex stainless steels are used in a variety of industries due to their high corrosion resistance. However, this is countered by a high coefficient of friction and thus a limited wear behaviour, which restricts the technical application possibilities. Coatings or conventional hardening processes, such as solution nitriding above 1000 °C, offer a certain reduction of these wear phenomena, but are associated with the risk of delamination and/or loss of corrosion properties. In addition, the hardening effect is limited for austenitic and duplex grades. The low temperature surface hardening process below 500 °C offers the possibility to overcome these limitations. In this article the technology of this process is explained. In addition, research results show the positive influence of this treatment on the lifetime of components made of corrosion resistant steels. As a future outlook, possible properties and applications for the prospective increasing number of hydrogen applications are explained.

Maintenance Policy with Lifetime Reduction Based on Uncertain Renewal Process

This paper focus on a (N, T) preventive maintenance (PM) policy with lifetime reduction discount rate. In our consideration, the lifetime of component is assumed to be an uncertain variable due to the absence of historical operational data, an uncertain (N, T) PM model with the lifetime reduction in a certain proportion is proposed based on uncertain renewal process. Accordingly, the uncertain model, which minimizes the expected maintenance cost rate, is formulated to find the optimal replacement cycle length T∗ and the number N∗ of preventive maintenance. Finally, a numerical example with sensitivity analysis of parameters is provided to illustrate the proposed model, the results imply that the parameters of cost and lifetime can significantly affect the optimal solutions N∗ and T∗, which can provide a useful reference and guidance for aircraft maintenance decision.

Challenges of reaching high renewable fractions in hybrid renewable energy systems

This study evaluates the techno-economic feasibility of hybrid renewable energy systems (HRES) for providing electricity in four example localities in the United States: western New York; San Diego, California; Milwaukee, WI; and the entire state of Texas. The Hybrid Optimization of Multiple Energy Resources (HOMER) Pro Microgrid Tool was used to simulate and assess a grid model relying on solar and wind electric generation with utility-scale battery storage as back-up to serve the load on an hourly basis, when renewable resources are not available. A total of 495 HOMER trials were modeled to determine the levelized cost of electricity (LCOE) and societal cost of electricity (SCOE) for each of these locations assuming varying levels of carbon taxes, the economic value of health benefits from emissions savings, and a renewable fraction (RF) ranging from 0% to 100%. Technical and financial properties for the model, such as individual component cost, life-time, and efficiency, were obtained from the U.S. Energy Information Administration (EIA). Emission rates for various generation sources were obtained from the U.S. Environmental Protection Agency (EPA) and health benefits were analyzed using the Co-Benefit Risk Assessment (COBRA) tool. Finally, the ideal renewable fraction resulting in the lowest LCOEs were obtained for each of the four locations studied. For carbon tax values of $0/tonne and $130/tonne, this was determined to be 34% to 48% for New York; 0% to 34% for San Diego; 55% to 75% for Milwaukee; and 21% to 65% for Texas. Applying health benefits can shift the optimal RF of HRESs to higher amounts by 5.26% on average.

Modeling and analysis for a repairable system with multi-state components under K-mixed redundancy strategy

In this paper, a three components repairable system with K-mixed redundancy strategy is proposed, in which the lifetimes of components, the repair time of failure components and the vacation time are distributed with different phase-type (PH) distributions. The different phases can represent different operational levels, repair levels and vacation levels. The multiple vacation policy is also adopted so that the human resources can be fully utilized. The repairable system is studied in both transient and stationary regimes with the matrix-analytic method, and not only some traditional reliability indexes are obtained, but also several new reliability indexes are obtained by employing Kronecker operator theory and aggregated stochastic theory. Finally, a numerical example is implemented to illustrate the results obtained in the paper.

Mechanical white etching layer formation kinetics in pearlitic steels: A phenomenological model based on microstructural characterization

In order to predict the lifetime of railtrack components, numerical models are required to better describe the apparition of microstructural defects that lead to material failure. In pearlitic steels, the severe mechanical loading or/and the local temperature increase result in the formation of a hard and brittle phase that is prone to cracking, which is called White Etching Layer (WEL).The current study proposes a phenomenological model, based on the microstructural evolution, to describe the mechanically-induced-WEL kinetics of formation. First, a detailed multiscale microstructural characterization was performed in order to identify suitable microstructural indicators for the WEL formation. The grain size, orientation and morphology, and internal disorientation were characterized for different steps of mechanical WEL formation. This could be achieved thanks to the use of a dedicated test bench that allows to monitor the wheel–rail contact condition (sliding, number of cycles, and contact pressure) independently. The proposed model was validated using tests performed in extreme load and sliding conditions.The numerical and experimental results indicate that the most severe conditions (contact pressure and sliding ratio) catalyze WEL formation, and that the same deformation state can be achieved through different loading paths.

Reinforcement Learning-Based Joint Reliability and Performance Optimization for Hybrid-Cache Computing Servers

Computing servers play a key role in the development and process of emerging compute-intensive applications in recent years. However, they need to operate efficiently from an energy perspective viewpoint, while maximizing the performance and lifetime of the hottest server components (i.e., cores and cache). Previous methods focused on either improving energy efficiency by adopting new hybrid-cache architectures including the resistive random-access memory (RRAM) and static random-access memory (SRAM) at the hardware level, or exploring tradeoffs between lifetime limitation and performance of multicore processors under stable workloads conditions. Therefore, no work has so far proposed a co-optimization method with hybrid-cache-based server architectures for real-life dynamic scenarios taking into account scalability, performance, lifetime reliability, and energy efficiency at the same time. In this article, we first formulate a reliability model for the hybrid-cache architecture to enable precise lifetime reliability management and energy efficiency optimization. We also include the performance and energy overheads of cache switching, and optimize the benefits of hybrid-cache usage for better energy efficiency and performance. Then, we propose a runtime <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> -learning-based reliability management and performance optimization approach for multicore microprocessors with the hybrid-cache architecture, jointly incorporated with a dynamic preemptive priority queue management method to improve the overall tasks’ performance by targeting to respect their end time limits. Experimental results show that our proposed method achieves up to 44% average performance (i.e., tasks execution time) improvement, while maintaining the whole system design lifetime longer than five years, when compared to the latest state-of-the-art energy efficiency optimization and reliability management methods for computing servers.

Microstructural changes in nuclear graphite induced by thermal annealing

Irradiation-induced property change in nuclear graphite is particularly important when considering the in-service lifetimes of graphite components. In other works, it has been shown that annealing of irradiated graphite above the irradiation temperature may heal atomic-level defects and thus reverse some amount of physical property change. In this work, virgin nuclear graphite IG-110 was annealed at 2500 °C to observe any microstructural changes due solely to high-temperature thermal annealing. The results shown in this study suggest that fullerene-like defects, which are not observed in as-prepared nuclear graphites, will arise due to thermal annealing near graphitization temperature. Consequently, such defects may directly contribute to non -recoverable physical property change which has previously been observed in irradiated nuclear graphites. • Non-recoverable physical property changes to nuclear graphite. • High-temperature thermal annealing of nuclear graphite. • Microstructural changes induced solely by high-temperature thermal annealing. • Fullerene-like defects characterized via transmission electron microscopy.

Phasor Analysis Reveals Multicomponent Fluorescence Kinetics in the LH2 Complex from Marichromatium purpuratum.

We investigated the fluorescence kinetics of LH2 complexes from Marichromatium purpuratum, the cryo-EM structure of which has been recently elucidated with 2.4 Å resolution. The experiments have been carried out as a function of the excitation density by varying both the excitation fluence and the repetition rate of the laser excitation. Instead of the usual multiexponential fitting procedure, we applied the less common phasor formalism for evaluating the transients because this allows for a model-free analysis of the data without a priori knowledge about the number of processes that contribute to a particular decay. For the various excitation conditions, this analysis reproduces consistently three lifetime components with decay times below 100 ps, 500 ps, and 730 ps, which were associated with the quenched state, singlet-triplet annihilation, and fluorescence decay, respectively. Moreover, it reveals that the number of decay components that contribute to the transients depends on whether the excitation wavelength is in resonance with the B800 BChl a molecules or with the carotenoids. Based on the mutual arrangement of the chromophores in their binding pockets, this leads us to conclude that the energy transfer pathways within the LH2 complex of this species differ significantly from each other for exciting either the B800 BChl molecules or the carotenoids. Finally, we speculate whether the illumination with strong laser light converts the LH2 complexes studied here into a quenched conformation that might be related to the development of the non-photochemical quenching mechanism that occurs in higher plants.

A Probabilistic Model for Forging Flaw Crack Nucleation Processes for Heavy Duty Gas Turbine Rotor Operations

Abstract We present a probabilistic model for quantifying the number of load cycles for nucleation of forging flaws—for a 3.5NiCrMoV high strength low alloy rotor steel—into a crack under gas turbine operating conditions. The model correlates low cycle fatigue data, ultrasonic testing indication data, flaw morphology, and type with the nucleation process. This paper is the third of a series of publications presenting this modeling approach progressively. It focuses on the effect of temperature variation on the nucleation life of forging flaws. We quantified the number of cycles to crack nucleation was for specimens that included forging flaws at elevated temperatures. Flaws of different sizes and shapes are effectively described at respective temperature and stress levels by either an ellipsoidal finite element model or an analytical area-based model. A local probabilistic low-cycle fatigue model analyzes the resulting stress distributions accounting for statistical size effects. Via Maximum Likelihood Estimation of these probabilistic low cycle fatigue results, a probabilistic model for crack nucleation of forging flaws is obtained. This proposed probabilistic model is based on experimental data for realistic heavy duty gas turbine rotor temperature and stress conditions. It can be utilized in the energy sector for component life time quantification. Our suggested approach can support component assessment under flexible gas turbines operation conditions driven by increased availability of intermittent renewable energy sources.

Probabilistic failure assessment of an irradiated DEMO breeding blanket component under ferromagnetic loads: Impacts of material data scattering and uncertainty in local stress intensities

The most significant technical challenge in developing structural materials for in-vessel components in the Demonstration Power Plant (DEMO) fusion reactor is to qualify the lifetime of material to guarantee the lifetime of components. The qualification needs to be conducted theoretically rather than empirically because it is conducted based on the knowledge and data acquired in fission neutron irradiation experiments and various simulation irradiation experiments rather than in experiments performed in the actual fusion environment. Such experiments will not be achievable until the DEMO fusion reactor becomes operational. Consequently, various uncertainties are expected in irradiation data and loading conditions.The probabilistic approach, where the probability of failure is calculated based on the probability density function of postulated load distribution and material property distribution, is one path to mitigate such uncertainties. In this approach, those probabilities constitute the subjective probability based on the theoretical understanding of fusion neutron irradiation effects on materials to maximize the confidence in the estimated value.A case study of the Japanese DEMO breeding blanket is the basis for the discussion of the technical issues involved in the probabilistic approach. The breeding blanket design was simplified, the failure probability was estimated, and the impact of electromagnetic force on ferromagnetic material caused by a strong magnetic field induced by toroidal field coils was considered. The discussion of the impact of the irradiation damage is based on the irradiation data for F82H reduced-activation ferritic/martensitic steel. A direction for the development of fusion structural materials is suggested in terms of design technology and the statistical quality of the irradiation database.

On Reliability Function of a k-out-of-n System with Decreasing Residual Lifetime of Surviving Components after Their Failures

We consider the reliability function of a k-out-of-n system under conditions that failures of its components lead to an increase in the load on the remaining ones and, consequently, to a change in their residual lifetimes. Development of models able to take into account that failures of a system’s components lead to a decrease in the residual lifetime of the surviving ones is of crucial significance in the system reliability enhancement tasks. This paper proposes a novel approach based on the application of order statistics of the system’s components lifetime to model this situation. An algorithm for calculation of the system reliability function and two moments of its uptime has been developed. Numerical study includes sensitivity analysis for special cases of the considered model based on two real-world systems. The results obtained show the sensitivity of system’s reliability characteristics to the shape of lifetime distribution, as well as to the value of its coefficient of variation at a fixed mean.

Design study for the lifetime of double-sided irradiated absorber tubes

The world is in need of sustainable and cost efficient supply of electrical energy. One important technology could be solar power towers, because of their base load capability. Even though this technology has seen a significant decrease in installation and operation costs, further cost reduction is necessary to reach a higher market share.This study investigates double-sided irradiated absorber tubes to reduce installation costs of molten salt receivers. With a re-arrangement of the tubes towards a star-shaped layout, the required number of the expensive absorber tubes could be halved. This study introduces and uses a vivid methodology, based on linear damage accumulation that allows for the calculation of damage proportions, as well as the expected lifetime of receiver components in years. The calculations show the lifetime of double-sided irradiated tubes to be about ten times higher than for those irradiated from one side. This enables a change in material towards cost efficient austenitic stainless steels, offering an additional option for cost savings. However, it is also outlined that particular attention has to be payed to the aiming point optimization of the heliostat field, because the irradiation has to be quite smooth and uniform on both sides of the tubes to extend the lifetime.

Fascinating physics at the edge of magnetic fusion devices

The physics of the processes at the edge of magnetic fusion devices is multifaceted and exhibits complex, nonlinear synergistic effects. Even though this region occupies only a small portion of the whole device, it plays a crucial role in overall plasma confinement, heat exhaust, and plasma–wall interactions. The latter affects not only the performance but also the lifetime of plasma-facing components and therefore remains an outstanding challenge for future fusion reactors. At the edge of fusion devices, researchers are dealing with phenomena including classical and anomalous plasma transport, atomic physics effects, and physics of plasma-facing material under strong irradiation by particle and energy fluxes. The diversity of edge physics makes it particularly attractive for young scientists. Working in this field, they can find endless possibilities to demonstrate their talents and creativity. This short review describes just some of the basic scrape-off layer and divertor plasma phenomena including divertor plasma detachment, intermittent bursts of anomalous cross-field plasma transport, plasma–material interactions, and dust in fusion plasmas, which are of particular interest in relation to fusion reactors.

Predictive Modeling of Local Film-Cooling Flow on a Turbine Rotor Blade

Abstract In the turbine section of a modern gas turbine engine, components exposed to the main gas path flow rely on cooling air to maintain hardware durability targets. Therefore, monitoring turbine cooling flow is essential to the diagnostic and prognostic efficacy of a condition-based operation and maintenance (CBOM) approach. This study supports CBOM goals by leveraging supervised machine learning to estimate relative changes to local film-cooling flowrate using surface temperature measured on the pressure side of a rotating turbine blade operating at engine-relevant aerothermal conditions. Throughout the lifetime of a film-cooled turbine component, characteristics of the film-cooling flow—such as film trajectory and cooling effectiveness—vary as degradation-driven geometry distortions occur, which ultimately affects the relationship between the model input and the model output—film-cooling flowrate predictions. The present study addresses this complication by testing a data-driven model on multiple turbine blades of the same nominal design, but with each blade exhibiting different localized film-cooling flow characteristics. By testing the model in this manner, strategies for mitigating the detrimental effects of film-cooling flow characteristic variations on model performance were investigated, and the corresponding flowrate prediction accuracy was quantified.

Liquid lithium as divertor material to mitigate severe damage of nearby components during plasma transients

The successful operation of thermonuclear fusion reactors such as ITER, DEMO, and future commercial plants is mainly determined by the optimum choice of materials for various components. The objective of this work is to accurately and comprehensively simulate the entire device in 3D to predict pros and cons of various materials, e.g., liquid lithium in comparison to tungsten and carbon to predict future ITER-like and DEMO divertor performances. We used our comprehensive HEIGHTS simulation package to investigate ITER-like components response during transient events in exact 3D geometry. Starting from the lost hot core plasma particles through SOL, deposition on the divertor surface, and the generation of secondary plasma of divertor materials. Our simulations predicted significant reduction in the heat loading and damage to the divertor nearby and internal components in the case when lithium is used on the divertor plates. While if tungsten or carbon are used on the divertor plate, significant melting areas and vaporization spots can occur (less for carbon) on the reflector, dome, and stainless steel tubes, and even parts of the first walls can melt due to the high radiation power of the secondary divertor plasma. Lithium photon radiation deposition into the divertor and nearby surfaces was decreased by two orders of magnitude compared to tungsten and by one order of magnitude compared to carbon. This analysis showed that using liquid lithium for ITER-like surfaces and future DEMO can lead to significant enhancement in components lifetime.

High-resolution secretory timeline from vesicle formation at the Golgi to fusion at the plasma membrane in S. cerevisiae.

Most of the components in the yeast secretory pathway have been studied, yet a high-resolution temporal timeline of their participation is lacking. Here, we define the order of acquisition, lifetime, and release of critical components involved in late secretion from the Golgi to the plasma membrane. Of particular interest is the timing of the many reported effectors of the secretory vesicle Rab protein Sec4, including the myosin-V Myo2, the exocyst complex, the lgl homolog Sro7, and the small yeast-specific protein Mso1. At the trans-Golgi network (TGN) Sec4's GEF, Sec2, is recruited to Ypt31-positive compartments, quickly followed by Sec4 and Myo2 and vesicle formation. While transported to the bud tip, the entire exocyst complex, including Sec3, is assembled on to the vesicle. Before fusion, vesicles tether for 5 s, during which the vesicle retains the exocyst complex and stimulates lateral recruitment of Rho3 on the plasma membrane. Sec2 and Myo2 are rapidly lost, followed by recruitment of cytosolic Sro7, and finally the SM protein Sec1, which appears for just 2 s prior to fusion. Perturbation experiments reveal an ordered and robust series of events during tethering that provide insights into the function of Sec4 and effector exchange.