Lifetime Of Components Research Articles

Enhanced creep lifetime in P91 steel weldments via stabilizing tempered martensite structure

P91 steel weldments are susceptible to Type IV creep cracking during high-temperature service, significantly reducing the creep lifetime of impacted components. For enhancing the creep lifetime of P91 steel weldments, the present work proposes a novel post-weld heat treatment strategy to stabilize the tempered martensite structure and avoid Type IV creep cracking. Compared to conventional post-weld tempered treatment weldments, the creep lifetime of as-welded weldment is improved by 1.7 times, while the creep lifetime of weldment subjected to post-weld normalizing followed by tempering is enhanced by 4.6 times, effectively preventing Type IV cracking. It has been revealed that creep weakness zones, that is, soft zones, occur in as-welded weldment and post-welded tempering treatment weldment, where the microstructure is predominantly recrystallized ferrites. Creep fracture always occurs in the region of the highest fraction of recrystallized grains. Post-weld normalizing and subsequent tempering can enhance prior austenite grain size and stabilize tempered martensite structure. For as-welded weldment and post-welded tempering treatment weldment, creep cavities preferentially grow along ferrite grain boundaries as compared to prior austenite grain boundaries, which could easily lead to intergranular premature cracking. For post-weld normalizing and subsequent tempering weldment, cavities form along prior austenite grain boundaries of base metal and are elongated together with martensitic packets/blocks under stress. Finally, the final fracture is caused by the rupture of elongated grains.

The infrared thermography system on the MAST-U tokamak

Power loading from plasma in the scrape-off layer limits the lifetime of plasma-facing components in tokamak-based power plants. The Mega Ampere Spherical Tokamak Upgrade [W. Morris et al., IEEE Trans. Plasma Sci. 46(5), 1217–1226 (2018)] (MAST-U) features four divertor strike points (SP) owing to its up-down symmetry. This paper introduces the five-camera infrared thermography system, covering all four SPs and their mode of operation on MAST-U. The system employs both medium and long wavelength cameras, offering high frame rates up to 4 kHz and spatial resolutions of down to 3 mm. Postprocessing involves artifact elimination and heat flux calculation using in-house analysis software that incorporates the inverse heat transfer code, THEODOR (THermal Energy Onto DivertOR).

Repair of heat load damaged plasma–facing material using the wire-based laser metal deposition process

Due to its unique properties tungsten is a promising candidate as plasma-facing-material (PFM) in future nuclear fusion reactors. Tungsten features an exceptionally high melting point, high thermal conductivity, low tritium inventory and comparatively low erosion rate under plasma loading [1]. But given the extreme loads on the PFM during operation of a fusion reactor, the lifetime of plasma-facing components (PFC)s is limited. Currently, it is planned to replace damaged PFCs when they reach the end of their service life. However, the lifetime of PFCs could be increased by in situ repair using additive manufacturing technology (AM) in the form of direct-energy-deposition (DED). The wire–based laser metal deposition process (LMD-w) meets several necessary conditions for operation in the vessel and could be used for performing such in situ repairs.It was investigated if the LMD-w process is able to heal thermal induced surface cracks and roughening by remelting the substrate during deposition of tungsten. For this purpose, tungsten samples of 12 × 12 × 5mm3, which later served as substrate plates for the LMD-w experiments, were treated with combined steady-state and transient thermal loads in the electron beam facility JUDITH 2. These samples were brazed to a copper cooling structure and exposed to 105 thermal shocks of 0.5 ms duration and an intensity of Labs = 0.55 GW m−2 (FHF = 12 MW s0.5 m−2) at a base temperature of Tbase = 700 °C. This way, edge localized mode (ELM) like thermal load damage was induced on the tungsten samples. On these samples, different LMD-w and laser remelting process strategies were performed. Subsequently, these samples were analyzed, and it was examined that the healing of the pre-damaged substrate material was successful. In parallel, the laser remelting process was modeled in a thermal transient finite element method(FEM) simulation in order to gain an insight into the temperatures prevailing in the material during the process.

Investigating the exciton dynamics in InGaN/GaN core-shell nanorods using time-resolved cathodoluminescence.

This study examines the exciton dynamics in InGaN/GaN core-shell nanorods using time-resolved cathodoluminescence (TRCL), which provides nanometer-scale lateral spatial and tens of picoseconds temporal resolutions. The focus is on thick (>20 nm) InGaN layers on the non-polar, semi-polar and polar InGaN facets, which are accessible for study due to the unique nanorod geometry. Spectrally integrated TRCL decay transients reveal distinct recombination behaviours across these facets, indicating varied exciton lifetimes. By extracting fast and slow lifetime components and observing their temperature trends along with those of the integrated and peak intensity, the differences in behaviour were linked to variations in point defect density and the degree and density of localisation centres in the different regions. Further analysis shows that the non-polar and polar regions demonstrate increasing lifetimes with decreasing emission energy, attributed to an increase in the depth of localisation. The semi-polar facet instead showed a spectral independence of the lifetime which could not be rationalised by an absence of exciton localisation. This investigation provides insights into the intricate exciton dynamics in InGaN/GaN nanorods, offering valuable information for the design and development of optoelectronic devices.

Data-driven evaluation of the Paris’ law parameters in polyethylene pipe grades — Increasing the precision of fracture mechanical lifetime estimation

The Paris’ Law parameters A and m are a necessity for predicting lifetimes of structural components under static or fatigue loading that fail due to crack initiation and propagation. Conventional methods require measurements of crack growth kinetics that involve direct or indirect monitoring of physical crack extension during long-term experiments. Usually, measurement series also involve multiple specimens in order to obtain a crack growth controlled failure diagram of an investigated material under relevant load conditions. In this contribution a combination of simple numerical, statistical and analytical approaches is presented to obtain A and m without the need to measure actual crack growth. This is accomplished by reformulating the Paris’ Law to express A as a function of m. The parameter m is varied within a reasonable range to generate an analytical function for A that solves the equation of the Paris’ Law based lifetime for a single specimen. A subsequent superposition of all available specimens reveals an intersection of all A functions at the technically relevant pair of A and m values that are capable of describing the lifetime of all specimens with a minimum error. The obtained best-fitting A and m are in good agreement with literature and are able to predict the lifetime of previously published sample data based upon cyclic Cracked Round Bar test results with an average error of 3.30 ± 2.67%.

Understanding Environmental Barrier Coating Lifetimes and Performance for Industrial Gas Turbines

Abstract Hydrogen or hydrogen blend fuels are expected to replace natural gas in land-based industrial gas turbines (IGTs) to support a greener power economy. Silicon carbide (SiC) base ceramic matrix composites (CMCs) are considered for replacement of Ni-based superalloys to facilitate future efficiency improvements. SiC CMCs require environmental barrier coatings (EBCs) to mitigate volatilization from high-temperature steam, thus making the EBC lifetime critical information for identifying CMC component lifetimes. The goal of this project is to determine the maximum bond coating temperature underneath the EBC for achieving an IGT component lifetime goal of 25,000 h, which is far greater than current CMC component lifetime requirements for aeroturbine applications. To provide data for the lifetime model, laboratory testing used atmospheric plasma-sprayed rare-earth silicate EBCs on monolithic SiC substrates with an intermediate Si bond coating. Specimens exposed to 1-h thermal cycles in flowing air–steam environments and reaction kinetics were assessed from 700 °C to 1350 °C by measuring the thickness of the thermally grown silica scales. The silica growth and phase transformation appear critical in predicting EBC lifetime and several strategies have been explored to reduce the oxide growth rate and improve EBC durability at elevated temperatures. Advanced characterization using Raman spectroscopy has helped clarify this system.

Intramolecular benzene excimer formation in 13,14-diphenyldibenzo[b,j][4,7]phenanthroline.

13,14-diphenyldibenzo[b,j][4,7]phenanthroline (DBP3) in various solvents was studied by time-resolved fluorescence and fs transient absorption (fs-TA) spectroscopy. An intramolecular benzene excimer is demonstrated to form within DBP3; it exhibits strong redshifted emission with maximum at 540-640nm. "Intrinsic" fluorescence from DBP3 is dramatically quenched down to τ = 50-400fs in all the solvents studied. Fs-TA and time-resolved fluorescence spectra have proved that relaxed intramolecular benzene excimer is formed from S1 state via hot excimer state with three lifetime components: 50fs, ∼3.5ps, and ∼25ps, which are of the inertial (electronic) and diffusive parts of the relaxation due to solute-solvent interaction. Formation of triplet states via intersystem crossing was observed directly from the upper excited electronic states of DBP3.

Upconversion photoluminescence of Er-doped Bi$_{4}$Ti$_{3}$O$_{12}$ ceramics enhanced by vacancy clusters revealed by positron annihilation spectroscopy

Abstract Doping of rare earth elements into Bi$_{4}$Ti$_{3}$O$_{12}$ can significantly enhance the upconversion photoluminescence (UCPL) properties, but its structure-property relationship is still unclear. In this work, Er-doped bismuth titanate Bi$_{4-x}$Er$_{x}$Ti$_{3}$O$_{12}$ ($x$=0, 0.1, 0.2, 0.3, 0.4, 0.5) ceramics were synthesized via solid-state reaction method. The X-ray diffraction analysis confirmed the orthorhombic crystalline structure of the Bi$_{4-x}$Er$_{x}$Ti$_{3}$O$_{12}$ ceramics without any secondary phases. Experiments and calculations of positron annihilation spectroscopy were carried out to characterize their defect structure. The comparison between the experimental and calculated lifetime revealed that vacancy clusters were the main defects in the ceramics. The increase of the intensity of the second positron lifetime component (I$_{2}$) of Bi$_{3.5}$Er$_{0.5}$Ti$_{3}$O$_{12}$ ceramics indicated the presence of a high concentration of vacancy clusters. The UCPL spectra shown the sudden enhanced UCPL performance in Bi$_{3.7}$Er$_{0.3}$Ti$_{3}$O$_{12}$ and Bi$_{3.5}$Er$_{0.5}$Ti$_{3}$O$_{12}$ ceramics, which were consistent with the variation of the second positron lifetime component (I$_{2}$). These results indicate that the enhanced UCPL properties are influenced not only by the concentrations of rare earth ions but also by the concentration of vacancy clusters present within the ceramics.

A Step‐by‐Step Approach for Replacing Si‐IGBTs With SiC‐MOSFETs Modules in Industrial Power Converters

ABSTRACTThis work presents a step‐by‐step approach for replacing Si‐IGBTs with SiC‐MOSFETs modules in a 9‐kW commercial double‐conversion UPS. Incremental modifications are applied to the original system, considering variations in switching frequency and evaluating its influence on losses and total volume. Through the use of Si‐IGBT transistors and redesigning the system, the volume and losses are analyzed for switching frequencies between 10 and 17 kHz. The IGBT showed limitations around 17 kHz, with high losses due to tail current. With SiC‐MOSFETs, the switching frequency is increased, resulting in smaller filter volumes. The SiC module allowed operation at frequencies in the tens and hundreds of kHz, with relatively low switching losses, which significantly reduced the volume of filters and heat transfer systems. These technological advancements resulted in reductions of up to 78% in the total volume and improved efficiency, enabling operation at lower temperatures and potentially increasing the lifetime of components.

Circular Economy: The 4Rs reduce-reuse-recycle-recover

Abstract This article summarizes the lecture presented at the Net Built 2024 conference. The lecture addresses the unsustainability of the current linear economy, characterized by the “take, make, dispose” model, in light of environmental challenges. The inefficiencies of this system lead to increased energy consumption, elevated CO2 emissions, and the exacerbation of climate change. It examines the current state of design and construction with respect to climate change and sustainable resource management. Additionally, the lecture introduces a methodology that integrates technologies and design philosophies capable of driving significant positive change. By advocating for a transformative approach to the expected lifetime of buildings and components, this presentation explores new paradigms grounded in the principles of the circular economy. To illustrate these strategies and their outcomes, the author provides a series of case studies. The presentation delves into open methods and strategies for managing building systems, focusing on lifecycle impact, durability, serviceability, and obsolescence.

Repair alert model when the lifetimes are discretely distributed

This paper deals with the repair alert models. They are used for analyzing lifetime data coming from engineering devices under maintenance management. Repair alert models have been proposed and investigated for continuous component lifetimes. Existing studies are concerned with the lifetimes of items described by continuous distributions. However, discrete lifetimes are also frequently encountered in practice. Examples include operating a piece of equipment in cycles, reporting field failures that are gathered weekly, and the number of pages printed by a device completed before failure. Here, the repair alert models are developed when device lifetimes are discrete. A wide class of discrete distributions, called the telescopic family, is considered for the component lifetimes, and the proposed repair alert model is explained in detail. Furthermore, the problem of estimating parameters is investigated and illustrated by analyzing a real data set.

Bending fatigue behavior of metastable and stable austenitic stainless steels with different surface morphologies

AbstractThe surface morphology has a significant influence on the fatigue behavior of components. For austenitic stainless steels (ASSs), this issue is even more pronounced due to their metastability. Based on the complex deformation mechanisms of metastable ASSs, which include dislocation slip, deformation twinning, and deformation‐induced martensitic phase transformation, the metastable stainless steel AISI 347 was investigated in this study together with the stable AISI 904L as a reference material. Four‐point bending fatigue tests with load ratio R = 0.1 and testing frequency f = 10 Hz at ambient temperature were carried out on specimens with five technically relevant surface morphologies: mechanical polished, milled, microshot peened, laser shock‐peened, and ultrasonic modified. Systematic material characterizations were carried out to elucidate the crucial role of surface roughness and deformation‐induced α′‐martensite in the fatigue behavior of both metastable and stable materials. While surface roughness is a well‐known key factor in conventional fatigue cases, deformation‐induced martensite layers implemented by various surface modification methods were proven to improve the fatigue life in metastable austenitic steels, opening new perspectives to extend the lifetime of ASS components.

Fitness consequences of depressive symptoms vary between generations: Evidence from a large cohort of women across the 20th century.

Depression has strong negative impacts on how individuals function, leading to the assumption that there is strong negative selection on this trait that should deplete genetic variation and decrease its prevalence in human populations. Yet, depressive symptoms remain common. While there has been a large body of work trying to resolve this paradox by mapping genetic variation of this complex trait, there have been few direct empirical tests of the core assumption that there is consistent negative selection on depression in human populations. Here, we use a unique long-term dataset from the National Health and Nutrition Examination Survey that spans four generational cohorts (Silent Generation: 1928-1945, Baby Boomers: 1946-1964, Generation X: 1965-1980, and Millenials: 1981-1996) to measure both depression scores and fitness components (lifetime sexual partners, pregnancies, and live births) of women from the United States born between 1938-1994. We not only assess fitness consequences of depression across multiple generations to determine whether the strength and direction of selection on depression has changed over time, but we also pair these fitness measurements with mixed models to assess how several important covariates, including age, body mass, education, race/ethnicity, and income might influence this relationship. We found that, overall, selection on depression was positive and the strength of selection changed over time-women reporting higher depression had relatively more sexual partners, pregnancies, and births except during the Silent Generation when selection coefficients neared zero. We also found that depression scores and fitness components differed among generations-Baby Boomers showed the highest severity of depression and the most sexual partners. These results were not changed by the inclusion of covariates in our models. A limitation of this study is that for the Millenials, reproduction has not completed and data for this generation is interrupted by right censoring. Most importantly, our results undermine the common belief that there is consistent negative selection on depression and demonstrate that the relationship between depression and fitness changes between generations, which may explain its maintenance in human populations.

The influence of Nickel on the corrosion protection of FeCrNi alloys after breakaway corrosion at 600 °C

Breakaway corrosion of stainless steels remains a challenge for many industrial applications operating in harsh conditions. The lifetimes of metallic components are often determined by the corrosion propagation after breakaway. Nevertheless, studies on the protective properties of the Fe-rich oxides formed after breakaway are scarce. This study investigates the influence of Ni on the protection after breakaway on a broad range of Fe18CrxNi model alloys, by systematically inducing breakaway of the initially formed protective, Cr-rich oxides. The results clearly demonstrate an improved protection after breakaway for higher Ni-contents, explained by the alloys’ ability to avoid internal oxidation involving Fe-rich BCC and spinel.

Stochastic ordering results on extreme order statistics from dependent samples with Archimedean copula

This paper considers parallel and series systems with heterogeneous components having dependent exponential lifetimes. The underlying dependence is assumed to be Archimedean and the component lifetimes are supposed to be connected according to an Archimedean copula. Sufficient conditions are found to dominate a parallel system with heterogenous exponential components, with respect to the dispersive order, by another parallel system with homogenous exponential components where the dependence structure between lifetimes of components is the same. We also compare two series systems (and two parallel systems) with general one-parameter dependent components and with respect to the usual stochastic ordering. Examples are given to illustrate the theoretical findings.

Stochastic aspects of reversed aging intensity function of random quantiles

This paper studies some stochastic properties of random quantiles according to the newly defined reliability measure called reversed aging intensity function. Preservation property of reversed aging intensity order under random quantile is obtained and using it, a lower bound and an upper bound for the reversed aging intensity function of a random quantile are derived. Preservation of two related monotonic reliability classes under random quantiles is also studied. We finally apply our results for reliability analysis of series systems with heterogeneous component lifetimes. Examples are included to examine and analyze the obtained results.

Ortho-positronium lifetime for soft-tissue classification

The objective of this work is to showcase the ortho-positronium lifetime as a probe for soft-tissue characterization. We employed positron annihilation lifetime spectroscopy to experimentally measure the three components of the positron annihilation lifetime—para-positronium (p-Ps), positron, and ortho-positronium (o-Ps)—for three types of porcine, non-fixated soft tissues ex vivo: adipose, hepatic, and muscle. Then, we benchmarked our measurements with X-ray phase-contrast imaging, which is the current state-of-the-art for soft-tissue analysis. We found that the o-Ps lifetime in adipose tissues (2.54 ± 0.12 ns) was approximately 20% longer than in hepatic (2.04 ± 0.09 ns) and muscle (2.03 ± 0.12 ns) tissues. In addition, the separation between the measurements for adipose tissue and the other tissues was better from o-Ps lifetime measurement than from X-ray phase-contrast imaging. This experimental study proved that the o-Ps lifetime is a viable non-invasive probe for characterizing and classifying the different soft tissues. Specifically, o-Ps lifetime as a soft-tissue characterization probe had a strong sensitivity to the lipid content that can be potentially implemented in commercial positron emission tomography scanners that feature list-mode data acquisition.

Effect of helium bubbles on the mobility of edge dislocations in copper

Abstract Helium bubbles can form in materials upon exposure to irradiation. It is well known that the presence of helium bubbles can cause changes in the mechanical behavior of materials. To improve the lifetime of nuclear components, it is important to understand deformation mechanisms in helium-containing materials. In this work, we investigate the interactions between edge dislocations and helium bubbles in copper using molecular dynamics (MD) simulations. We focus on the effect of helium bubble pressure (equivalently, the helium-to-vacancy ratio) on the obstacle strength of helium bubbles and their interaction with dislocations. Our simulations predict significant differences in the interaction mechanisms as a function of helium bubble pressure. Specifically, bubbles with high internal pressure are found to exhibit weaker obstacle strength as compared to low-pressure bubbles of the same size due to the formation of super-jogs in the dislocation. Activation energies and rate constants extracted from the MD data confirm this transition in mechanism and enable upscaling of these phenomena to higher length-scale models.

Modeling plasticity-mediated void growth at the single crystal scale: A physics-informed machine learning approach

Modeling the evolution of voids during plastic flow as well as their effects on plastic dissipation is critical for both component manufacturing and lifetime estimation purposes. To this end, we propose a rate-dependent constitutive model to homogenize the effects of semi-randomly distributed voids on single crystal plasticity whilst capturing void interaction and plastic anisotropy. The present work focuses on the case of face centered cubic crystals to introduce an anisotropic gauge function applicable within the crystal plasticity formalism. The approach combines analytical methods to describe the micromechanics of the system in combination with symbolic regression to capture analytically intractable mechanisms from data. The hybrid framework uses a physics-informed genetic programming-based symbolic regression algorithm to solve a multiform optimization problem simultaneously producing a new gauge function and a new strain rate equation. This is also a multi-objective optimization problem with many competing objectives. A new search and selection step is introduced to the genetic algorithm that promotes convergence toward a global solution that better satisfies all the objectives. Overall, the symbolic equations produced leverage data-driven methods to achieve greater accuracy than comparable alternatives on an analytically intractable problem while maintaining model transparency.

Post-Processing of Inconel 718 Alloy Fabricated by Additive Manufacturing: Selective Laser Melting

The review analyses Inconel 718 (IN718) alloy, which is the nickel-based superalloy and has great application in industries due to its superior mechanical properties even at elevated temperatures by means of the solid-solution strengthening and precipitation strengthening. However, because of the tool over-wear, poor part surface integrity, high hardness and low thermal-conductivity properties, it is difficult to manufacture finished products with using conventional machining methods. It is especially urgent for the products of complex designs. In this regard, justification is given for the widespread use of modern additive manufacturing (AM) for the fabrication of the products from IN718. The most popular is AM based on the selective laser melting (SLM) technique, which can fabricate complex geometries with superior material properties. At the same time, the metal parts fabricated by SLM suffer from excessive residual porosity, residual tensile stress in the near-surface layer, and the formation of a relatively rough surface. In addition, the SLM-inherited surface defects can cause stress concentration to initiate cracks, reducing the fatigue strength of the printed parts. The review focuses on identifying potential solutions to the surface-finish complex additive manufactured to improve the surface properties to meet the industry requirements. Therefore, the improvement of the IN718-alloy-parts’ surface properties printed by the SLM becomes especially relevant. Currently, different surface post-processing technologies are being developed to obtain the expected surface quality of the SLM-components. As demonstrated, the finish surface enhancement treatments led to significant improvement in the wear resistance, corrosion resistance, increase in fatigue life, and tensile strength of the metallic materials. Therefore, adapting surface post-processing technologies has become a growing area of interest as an effective tool for improving the functionality and service lifetime of SLM IN718-alloy components. The review aims to analyse the main results of the most systematic studies of the currently developed surface post-treatments aimed to improving the surface-structure quality and properties of the IN718 parts fabricated by SLM. These results contribute to a better understanding of the role of the various-parameters’ effects on the surface improvements during the surface post-processing and changes in the structure–phase state, and physical, chemical and mechanical properties. Examples of the effects of a series of surface post-processing methods are presented: laser polishing, mechanical magnetic polishing, cutting finish-machining operations, shot peening, sandblasting technique, ultrasonic-impact treatment, and electrochemical polishing.