Lifetime Of Components Research Articles

Estimation of remaining useful lifetime of power electronic components with machine learning based on mission profile data

Estimation of remaining useful lifetime of power electronic components with machine learning based on mission profile data

On the number of failed components in a series–parallel system upon system failure when the lifetimes are DNID discrete random variables

In this paper, we study properties of a series–parallel system. The component lifetimes may be dependent and non-identically distributed (DNID) discrete random variables. We consider the number of failed components upon system failure. We derive the probability mass function and the expected value of this quantity. In addition, we find the conditional probabilities corresponding to this variate given some partial information about the system failure. We also provide a numerical example to demonstrate the theoretical results.

Interplay Between Strain and Thickness on the Effective Carrier Lifetime of Buffer-Mediated Epitaxial Germanium Probed by the Photoconductance Decay Technique

We report contactless effective minority carrier lifetime of epitaxially grown unstrained and in-plane <110> biaxially tensile-strained (001) germanium (ε-Ge) epilayers measured using microwave-reflectance photoconductance decay measurements. Strained Ge epilayers were grown using InxGa1–xAs linearly graded buffers on (001) GaAs substrates. Using homogeneous excitation of unstrained Ge epilayers, thickness-dependent separation of minority carrier lifetime components under low injection conditions yielded a bulk lifetime of 114 ± 2 ns and low surface recombination velocity of 21.3 ± 0.04 cm/s. More notably, an effective minority carrier lifetime of >100 ns obtained from sub-50 nm 1.6% tensile-strained Ge epilayers showed no degradation relative to the unstrained counterpart. Detailed material characterization using X-ray diffractometry revealed successful strain transfer of 0.61 and 0.89% to the Ge epilayers via InxGa1–xAs metamorphic buffers and confirms pseudomorphic growth. Lattice coherence observed at the ε-Ge epilayer and InxGa1–xAs buffer heterointerfaces via transmission electron microscopy substantiates the prime material quality achieved. The relatively high carrier lifetimes achieved are an indicator of excellent material quality and provide a path forward to realize low-threshold Ge laser sources.

Life cycle assessment and life cycle costing of a building-scale, solar-driven water purification system

Water purification systems require material resources and energy to build and operate, thus leading to environmental burdens. Mature water treatment technologies such as reverse osmosis and multi-effect distillation have been extensively studied for their environmental impacts. There is still a lack of such studies in one of the promising technologies, namely, air gap membrane distillation (AGMD). This study performs a cradle-to-grave life cycle assessment (LCA) and a life cycle costing of a solar-driven AGMD water purification system. This research also assesses the cost competitiveness of the system compared to local bottled water using a levelized cost of water (LCOW) approach. The study shows that the environmental impacts of the water purification systems (using a functional unit of 590 m3 of drinking water produced over a time period of 15 years) are: 27,224 kg CO2eq (climate change), 2,408 kg 1.4-DCB (human carcinogenic toxicity), 3,100 kg 1.4-DCB (marine ecotoxicity), and 2,286 kg 1.4-DCB (freshwater ecotoxicity). The solar PV sub-system and solar thermal sub-system have a much higher impact than the water purification sub-system. The LCOW calculations show that the system, with its current runtime of six hours using solar energy, has a levelized cost of 0.46 USD/L. Alternative scenarios, such as the use of grid electricity and end-of-life treatment of generated wastes, are also evaluated. A sensitivity analysis is performed on four parameters, i.e., component lifetime, maintenance frequency, discount rate, and AGMD module production cost. This study could be useful to local governments, investors, and potential customers interested in the water purification system's environmental footprint and cost competitiveness.

Role of Fe in long-range ordered Ni2Cr precipitates in Ni-Cr-Fe model alloys during isothermal aging

The precipitation of new phases during long-term service at elevated temperatures is a concern for the thermal stability of engineering alloys. In Ni-Cr-based alloys, e.g., Alloy 690, the formation of long-range ordered Ni2Cr causes embrittlement and may impact the lifetime of nuclear power plant components. In this work, we quantify the formation and evolution of Ni2Cr precipitation in eleven Ni-Cr-Fe model alloys with 0, 5, 7, and 10 wt % Fe contents, and with Ni/Cr atomic ratios of 1.8, 2.0, 2.2, 2.4. These alloys were isothermally aged up to 10,000 h at temperatures between 330 and 475 °C. The alloys were characterized by synchrotron-based x-ray diffraction and Vickers hardness testing to quantify Ni2Cr precipitate size, and the impact of precipitate size on the mechanical properties as a function of Fe content. After 10,000 h of aging at 475 °C and 418 °C, the formation of Ni2Cr was observed in all alloys with 0 and 5 wt % Fe. After 10,000 h of aging at 418 °C, Ni2Cr precipitates were also observed in the 7 wt % Fe containing Ni/Cr=2.0 sample. No clear evidence of Ni2Cr was observed in any of the 10 wt % Fe samples at any time and temperature combination. We find that the face-centered cubic matrix lattice contraction and Vickers hardness are correlated with the Ni2Cr formation. The greatest change in hardness and lattice contraction occurs in stoichiometric alloys (Ni/Cr=2.0) with 0 wt % Fe at 475 °C. The rate of change in the material properties for the 5 wt % Fe alloys is reduced, however the magnitude of changes is similar to 0 wt % Fe alloys. A precipitation hardening model developed for Ni-Cr alloys based on critical resolved shear stress with weakly coupled dislocations shows a clear link between Ni2Cr precipitate size and hardness. This trend held across all alloys with Ni2Cr formation regardless of Fe concentration. This important structure-property relationship can potentially help define Ni-Cr-Fe-based component lifetimes directly through an understanding of how Ni2Cr formation impacts mechanical properties as a function of Fe content.

LCA approach for environmental impact assessment within the maritime industry: Re-design case study of yacht’s superstructure

Sustainable development, one of the main challenges of our time, is a policy focused on the perfect balance between three fundamental pillars: environmental, economic and social sustainability. As regards the environmental protection, the Life Cycle Assessment (LCA) methodology allows to evaluate the sustainability profile of the overall Life-Cycle (LC) of products, processes and services, based on an inventory (in terms of materials/energy consumption and emissions/waste production) referred to all LC stages. The paper describes an application of LCA in the maritime transportation field, after a careful analysis of the state of the art. In particular, the case study consists in the environmental comparison of two alternative design solutions for the superstructure of a Azimut-Benetti yacht, designed by Corporate R&amp;D department and manufactured in one of Benetti botyards. The competing construction options are a Glass Fiber reinforced Vinylester-isophthalic Resin (GFVR) and a Carbon Fiber reinforced Epoxy Resin (CFER) component, and they are assessed in terms of Global Warming Potential through the CML2001 Life Cyle Impact Assessment (LCIA) method. The study takes into account the entire LC of the superstructure component, divided into production (including raw materials, manufacturing and transportations), use (including both fuel consumption and exhaust air emissions) and End-of-Life (EoL). The Life Cycle Inventory (LCI) is mainly based on primary data (materials and energy consumption for manufacturing) directly provided by the construction company; missing data are retrieved from secondary sources (literature and LCI database provided by the GaBi6 environmental software). Results show that, despite the higher impact in production stage, the innovative solution allows achieving a significant quota of GWP over the entire LC (more than 16%), which is mainly associated with decreased amount of fuel needed and lowered CO2 exhaust emissions during operation. The sensitivity analysis reveals that the environmental advantage provided by the CFER design becomes bigger as both component life-time and yacht consumption increase.

Stochastic comparison on active redundancy allocation to K-out-of-N systems with statistically dependent component and redundancy lifetimes

AbstractIn the literature on active redundancy allocation, the redundancy lifetimes are usually postulated to be independent of the component lifetimes for the sake of technical convenience. However, this unrealistic assumption leads to a risk of inaccurately evaluating system reliability, because it overlooks the statistical dependence of lifetimes due to common stresses. In this study, for k-out-of-n:F systems with component and redundancy lifetimes linked by the Archimedean copula, we show that (i) allocating more homogeneous redundancies to the less reliable components tends to produce a redundant system with stochastically larger lifetime, (ii) the reliability of the redundant system can be uniformly maximized through balancing the allocation of homogeneous redundancies in the context of homogeneous components, and (iii) allocating a more reliable matched redundancy to a less reliable component produces a more reliable system. These novel results on k-out-of-n:F systems in which component and redundancy lifetimes are statistically dependent are more applicable to the complicated engineering systems that arise in real practice. Some numerical examples are also presented to illustrate these findings.

Nuclear data for fusion: inventory validation successes and future needs

Nuclear data, describing neutron reaction probabilities (cross sections) and decay behaviour, are critical to the design and operation of fusion experiments and future fusion power plants. Equally vital, are the inventory codes that use the data to predict neutron-induced activation and transmutation of materials, which will define the radiological hazards that must be managed during reactor operation and decommissioning. Transmutation, including gas production, combined with the neutron-induced displacement damage, will also cause the properties of materials to degrade, for example through swelling and embrittlement, eventually limiting the lifetime of components. Thus validated and accurate nuclear data and inventory codes are essential. For data validation there are decay heat measurements performed at FNS in Japan more than 20 years ago. The experiments produced an invaluable database for benchmarking of nuclear data libraries; the latest versions of several international libraries perform well against this data during tests with the FISPACT-II inventory code, although there is still scope for improvement. A recent attempt to provide fusion-relevant validation based on γ-spectroscopy data from neutron-irradiated material samples tests produced predictions for short-lived (several hours or less) radionuclides. The detailed analysis performed for molybdenum demonstrates how these data could eventually provide a new benchmark, and also illustrates the potential benefits of further experiments targeting the longer-lived radionuclides relevant to maintenance and decommissioning timescales. There are also some successful tests of transmutation predictions with FISPACT-II. These direct validations of inventory simulations are critical for lifetime predictions and future experiments should learn lessons from the examples described for tungsten, which demonstrate the importance of an accurate description of the neutron spectrum in experiments. More novel experimental techniques are needed to measure helium production in materials such as Fe and C, but the need to validate the nuclear data evaluations used by simulations should motivate future experimental efforts.

Optimal task-driven time-dependent covariate-based maintenance policy

In this paper, a multi-component series system is considered. The system is monitored periodically. The exact cause of failure is assumed to be masked or missed. In the masked setup, the exact cause of failure is unknown but the set to which it belongs, called the masked set, is known. While in the missing setup, there is no information about the exact cause of failure. A time-dependent covariate-based maintenance policy is proposed such that the maintenance action and cost of the failed components at inspection times depend on several factors and can vary. The component lifetime distributions are considered unknown. The proposed maintenance policy is optimized using some task-driven decision-making statistical learning methods. Finally, the applicability of the proposed theory is analyzed through some numerical analysis. The results are compared to the case where lifetime distributions are known as a benchmark.

Single-Particle Dynamics of ZnS Shelling Induced Replenishment of Carrier Diffusion for Individual Emission Centers in CuInS2 Quantum Dots.

Insights into blinking and photoactivation of aqueous copper indium sulfide (CIS) quantum dots have been obtained using fluorescence correlation spectroscopy (FCS) and fluorescence lifetime correlation spectroscopy (FLCS). An unusual excitation wavelength-dependence of photoactivation/photocorrosion is manifested in an increase in the initial correlation amplitude G(0) for λex = 532 nm, but a decrease for λex = 405 nm. This has been rationalized in terms of different contributions from surface-assisted recombination in the two cases. Blinking times obtained from the autocorrelation functions (ACFs) of the 100-200 ns lifetime component (core Cu-mediated recombination) are almost unaffected by shelling, but those from the ACF for the 10-30 ns lifetime (surface states) increase significantly. Absence of cross-correlation between the two recombinative states of bare CIS QDs and the emergence of an anticorrelation with the introduction of the ZnS shell are observed, indicating the diffusive nature of the two states for CIS-ZnS. The diffusion is inhibited in bare CIS QDs due to the preponderance of surface states.

Influence of austempering temperature on carbide free bainite development, a critical review

In this review paper, it is well established that high carbon high silicon steels on austempering result in carbide free bainite (CFB) which exhibits enhanced mechanical and tribological properties without adding any heavy alloying elements. Most of the research has been pointed out regarding the improvement of CFB steels that consists of the fine structure of bainitic ferrite laths and retained austenite (RA). In some cases, it was observed that the tensile strength of CFB steels was found similar to the commercial quenched and tempered steel alloys. Regarding other properties, it is estimated that out of the various failures that take place due to wear, 50% are caused by abrasive wear. To improve the lifetime of components, the selection of material and optimized processing techniques plays a pivotal role.

Materials and Corrosion in Seawater Reverse Osmosis Plants: A Review

Desalination is emerging as one of the most promising solutions to extraction and increasing global demand for drinking water. A water purification process called reverse osmosis (RO), in which dissolved solids are separated from solutions by partially permeable membranes. Advances in membrane technology have resulted in the removal of up to 99% of salts in seawater. However, the process and system of seawater treatment RO are associated with many problems, such as scaling and fouling of the membranes, corrosion of the pumps, valves and piping system due to the highly concentrated salt solution and high chemical consumption. Nowadays, these problems have become very critical as they severely affect the desalination process and also massively deteriorate the performance and lifetime of the system components and materials. To ensure that the desalination process is always the best option for a low-maintenance, highly efficient and cost-effective system and process, a comprehensive study of these problems is essential. Therefore, this article addresses the characteristics of metallic materials and corrosion problems in the reverse osmosis process of seawater desalination, as well as the best solutions to focus on and evaluate for an optimal seawater desalination process, and the selection of the category of duplex stainless steels suitable for seawater desalination plants to reduce maintenance, avoid plant shutdown and ensure plant safety.

Anisotropic graphene films with improved thermal conductivity and flexibility for efficient thermal management

The rapid development of miniaturization and densification of electronic devices brings substantive needs for highly thermally conductive and flexible thermal interface materials (TIM) to ensure service reliability and prolong the lifetime of electronic components. Herein, we proposed highly thermally conductive and flexible graphene (Gr) films by a vacuum-assisted filtration strategy. Driven by the strong vacuum shear force and the dispersing effect of Polyvinyl pyrrolidone (PVP), the Gr sheets stacked layered-by-layered owing to hydrogen bond (H-bond). The highly laminated Gr/PVP films (GPVP-F) exhibited high in-plane thermal conductivity of 81.2 W m−1 K−1 and through-plane thermal conductivity of 5.1 W m−1 K−1. In actual applications, the GPVP-F cooled the light-emitting diode (LED) chip by 4.3 °C (from 46.1 °C to 41.8 °C) when being used as flexible TIM, which was at an advanced level for room-temperature device (＜ 50 °C) cooling. Besides, GPVP-F still performed excellent thermal conductivity (68.1 W m−1 K−1) even at 100 °C and splendid stability after 10 times of heating-cooling cycles. More importantly, the meritorious flexibility ensured GPVP-F being capable of applying in the device with irregular shapes. All the above results bring GPVP-F a promising prospect in thermal management of electronic devices.

Tribocorrosive Aspects of Tungsten Carbide, Silicon Nitride, and Martensitic Steel under Fretting-like Conditions

Water-based lubrication faces the common challenge of component lifetime extension which is impaired by tribocorrosion due to material surface depassivation. However, such mechanisms in a pH-neutral and low-halide electrolyte require additional understanding. A ball-on-flat configuration study of hard-phase materials in a low amplitude–high frequency sliding contact against martensitic chromium steel with contact pressures around 200 MPa is presented. Under lubrication by purified water, tungsten carbide-based metal matrix composite (MMC) with NiCr binder and silicon nitride-based ceramic (SiAlON) against DIN/EN 1.4108 steel yielded coefficients of friction above unity. Wear scar enlargement led to fretting-like conditions with adhesion becoming the fundamental wear mechanism. A tribocorrosion-induced depletion of tungsten carbide and nickel was determined for MMC. SiAlON materials suffered extreme wear under the formation of abrasive SiO2, while heat-treated DIN/EN 1.4125 steel showed lower friction and wear, but also showed signs of hydrogen embrittlement. Results from accompanying single-material corrosion experiments could not satisfactorily explain the phenomena. Including galvanic interaction and the influence of contact geometry, a new tribocorrosion model for fretting conditions is proposed. It describes an expanding anodic belt located at the inner-most crevice position of an otherwise cathodically polarized material. Low conductivity of the electrolyte is seen as a key player in this process, while the galvanic situation between two materials in contact was shown to invert when water was substituted by a wet organic phase.

Prognostics-based adaptive control strategy for lifetime control of wind turbines

Abstract. Variability in wind profiles in both space and time is responsible for fatigue loading in wind turbine components. Advanced control methods for mitigating structural loading in these components have been proposed in previous works. These also incorporate other objectives like speed and power regulation for above-rated wind speed operation. In recent years, lifetime control and extension strategies have been proposed to guarantee power supply and operational reliability of wind turbines. These control strategies typically rely on a fatigue load evaluation criteria to determine the consumed lifetime of these components, subsequently varying the control set point to guarantee a desired lifetime of the components. Most of these methods focus on controlling the lifetime of specific structural components of a wind turbine, typically the rotor blade or tower. Additionally, controllers are often designed to be valid about specific operating points and hence exhibit deteriorating performance in varying operating conditions. Therefore, they are not able to guarantee a desired lifetime in varying wind conditions. In this paper an adaptive lifetime control strategy is proposed for controlled aging of rotor blades to guarantee a desired lifetime while considering damage accumulation level in the tower. The method relies on an online structural health monitoring system to vary the lifetime controller gains based on a state-of-health (SoH) measure by considering the desired lifetime at every time step. For demonstration, a 1.5 MW National Renewable Energy Laboratory (NREL) reference wind turbine is used. The proposed adaptive lifetime controller regulates structural loading in the rotor blades to guarantee a predefined damage level at the desired lifetime without sacrificing the speed regulation performance of the wind turbine. Additionally, a significant reduction in the tower fatigue damage is observed.

Stochastic comparisons of lifetimes of fail-safe systems with dependent and heterogeneous components under random shocks

A fail-safe system is a ( n − 1 ) -out-of-n system whose lifetime is represented by the second-order statistic. This work studies stochastic comparisons of lifetimes of fail-safe systems with dependent and heterogeneous components, where the components are subjected to random shocks instantaneously. The results are derived for a general semiparametric family of distributions of the component lifetimes. We derive sufficient conditions for the comparison results under the usual stochastic order, and we provide counterexamples to show that under those conditions, similar comparisons cannot be made under the hazard rate order.

Likelihood inference for geometric lifetimes of components of [formula omitted]-out-of-[formula omitted] systems

This paper is concerned with maximum likelihood inference based on failure times of components of a k-out-of-n system registered up to and including the moment of the breakdown of the whole system. We assume that the component lifetimes are independent and have the same geometric distribution with an unknown parameter θ. We first find the maximum likelihood estimator (MLE) of θ. Then, restricting the attention to series systems, we derive some exact and asymptotic properties of the MLE of interest. Next, we generalize our results to the situation when we observe N independently working k-out-of-n systems rather than one such system. In particular, we describe the asymptotic behavior of the MLE of θ as N grows to infinity. Finally, we illustrate our theoretical results with some examples, tables and figures.

Near-Infrared Fluorescence Lifetime Imaging of Biomolecules with Carbon Nanotubes.

Single-walled carbon nanotubes (SWCNTs) are versatile near infrared (NIR) fluorescent building blocks for biosensors. Their surface is chemically tailored to respond to analytes by a change in fluorescence. However, intensity-based signals are easily affected by external factors such as sample movements. Here, we demonstrate fluorescence lifetime imaging microscopy (FLIM) of SWCNT-based sensors in the NIR. We tailor a confocal laser scanning microscope (CLSM) for NIR signals (>800 nm) and employ time correlated single photon counting of (GT)10 -DNA functionalized SWCNTs. They act as sensors for the important neurotransmitter dopamine. Their fluorescence lifetime (>900 nm) decays biexponentially and the longer lifetime component (370 ps) increases by up to 25 % with dopamine concentration. These sensors serve as paint to cover cells and report extracellular dopamine in 3D via FLIM. Therefore, we demonstrate the potential of fluorescence lifetime as a readout of SWCNT-based NIR sensors.

Stability of collagen gel after uv irradiation

Type I collagen is the most abundant extracellular matrix protein in the human body, as well as is the main structural element in tissues and regulates cellular functions. In lifetime, the organism and extracellular matrix components such as collagen are exposed to UV irradiation. The purpose of this work was to study the effect of UV irradiation on the stability and structure of collagen fibrils. It has been shown that UV irradiation has a stabilization effect on collagen gel at a concentration of 0.5 mg/ml. Scanning electron microscope images have shown that the diameter of the collagen fibrils is not changed after UV irradiation. The degree of spreading of cells cultured on collagen fibrils after UV irradiation is greater compared to those cultured on collagen fibrils unirradiated with UV light. UV irradiation promotes a shift of the collagen amide A band to lower frequency, indicating that it induces structural changes in collagen.

On conditional spacings from heterogeneous exponential random variables

The conditional spacings are investigated here based on a series system with n heterogeneous exponential component lifetimes. First, the survival function and the joint distribution of conditional spacings are obtained. Then, the survival function of the first spacing is shown to be Schur-convex in the hazard rates of component lifetimes. Further, some stochastic comparisons of spacings are carried out. Finally, some results for the conditional sample range are discussed.