Lifetime Extension Research Articles

Fatigue crack initiation and growth behavior within varying notch geometries in the low‐cycle fatigue regime for FV566 turbine blade material

AbstractPlain bend bars made from FV566 martensitic stainless steel were extracted from the root of ex‐service power plant turbine blades and several industry‐relevant notch geometries were introduced. Some of the samples were shot peened. The notched bend bars were loaded plastically in the low‐cycle fatigue regime and finite element (FE) modeling carried out to investigate the effects of changing notch geometry, combined with shot peening, on fatigue behaviors such as crack initiation, short crack growth, and coalescence. Shot peening damaged the notch surface, accelerating initiation behaviors, but had a lifetime‐extending effect by retarding short crack growth in all tested notch geometries. At a total strain range higher than 1.2%, the lifetime extension benefit from shot peening was diminished due to compressive residual stress relaxation in the notch stress field. Notch geometry (and the associated varying constraint levels and stress/strain gradients) was found to have no notable difference on fatigue life when tested at identical notch‐root strain ranges.

Sleep-wakeup scheduling algorithm for lifespan maximization of directional sensor networks: a discrete cuckoo search optimization algorithm

Directional sensor networks (DSNs) are ad-hoc networks which are utilized in different industrial applications. Their usual engagements are to monitor and to perform the coverage of all specific targets in the observing fields permanently. These kinds of networks include numerous configurable directional sensors in which they can be utilized in one of the possible directions along with the one of their adjustable ranges. Although the energy harvesting methodology is being applied for these battery-hungry applications, the battery management and network lifetime maximization are still prominent challenges. In this paper, the network lifetime extension is formulated to a discrete optimization problem which is a famous non-deterministic polynomial time hardness (NP-Hard) problem. To solve this combinatorial problem, a discrete cuckoo search algorithm (D-CSA) is designed and is called in several rounds. A cover is a sub set of configured sensors capable of monitoring all targets in the observing field. In each round, the most efficient cover is constituted along with its activation time. In the determined activation time, the sensors in the cover are scheduled in wakeup mode whereas others are set in sleep mode to save energy. Despite other meta-heuristic algorithms, this proposed algorithm utilizes the novel defined discrete walking around procedures that makes to reach a good balance between exploration and exploitation in this complex search space. The proposed algorithm has been tested in different scenarios to be evaluated. The simulation results in the variety circumstances prove the superiority of the proposed algorithm is about 20.29%, 19.55%, 14.40%, 14.51%, 7.70% and 8.03% in term of average lifespan improvement against H-MNLAR, Hm-LifMax-BC, GA, ACOSC, H-GATS, and HDPSO algorithms, respectively. The results also show the high potential scalability of the proposed algorithm.

Capacitor Lifetime Extension of Interleaved DC–DC Converters for Multistring PV Systems

Interleaved dc-dc converters are being vastly applied for a wide range of applications. Inherent power sharing between the power modules and reduction of the output waveforms ripple are the main advantages of these power systems. However, in some cases, such as the multi-string photovoltaic converters, each power module manages different power leading to an unbalanced operation of the interleaved converters. In this case, the harmonic response of the conventional interleaving operation is degraded. This fact affects directly the expected lifetime of the dc-link capacitor of the power converter which is one critical component of the system. In this paper, a variable-angle phase displacement angle is proposed in order to mitigate this problem achieving an extension of the converter lifetime.

Effect of curtailment scenarios on the loads and lifetime of offshore wind turbine generator support structures

Curtailment is a known phenomenon for wind turbine operators of both onshore and offshore wind turbine generators (WTG). Curtailment refers to the situation in which the power output of all WTG’s within a windfarm is forced below the expected power output at the occurring environmental conditions. A direct consequence of curtailment is the loss of power production. In the present contribution further consequences of curtailment of an offshore wind farm (OWF) are studied from the perspective of the support structure, in specific the foundation. In relation to curtailment a couple of potentially critical operational conditions impacting the fatigue consumption of the support structure can be identified. Besides the standstill during operational windspeed conditions, in specific damaging for the +7MW generation WTG’s, curtailment introduces repeated transitions between operational conditions. Since transitions between operational conditions of a WTG are known to be a cause of high fatigue loads in the structural components of the WTG, their increased occurrence due to curtailment might also have an impact on the fatigue consumption of the support structure. With the growing interest of the industry to quantify and potentially optimize the structural lifetime consumption in view of potential lifetime extension of OWF assets, any potential fatigue damaging operational condition is to be investigated. The present work focusses on the investigation of the impact these transitional load cycles may have on the structural lifetime of the WTG foundation. To assess the impact on lifetime, the assessment of the damage equivalent loads (DEL) derived from structural health monitoring (SHM) data are used as a data-driven alternative for model-based load simulations. In the present work such data-driven lifetime assessment studies the impact of curtailment regimes with different frequency of stop and start cycles on the structural lifetime. The study is performed based on 1 year of SHM data collected from two OWF’s. The assessment demonstrates that the impact of additional transitional load cycles on the structural fatigue life consumption is to be considered when defining a long-term curtailment strategy for an OWF.

From an Environmental Viewpoint Large ICT Networks Infrastructure Equipment must not be Reused

Circular strategies must and will vary for different product groups. Life Cycle Assessment (LCA) will help show which is the best strategy in any given situation as not all Circular Economy initiatives lead to universal sustainability benefits. There is a misunderstanding that lifetime extension via remanufacturing and refurbishment is ecologically effective for Business’, ’to’, ’Business ICT goods like ICT network infrastructure (ICTNI) products. This is shown herein by typical relations between manufacturing and the use of environmental impact for ICTNI products as a function of the energy efficiency and lifetime of the product at hand and the next corresponding product model. Full LCA would come to the same conclusion, as the ratio between the use stage and the production stage will not change dramatically. To avoid doing very significant harm to the environment, older than 5 years ICTNI products must not be reused. The reasons are that the energy efficiency improvement rate of the following generation of most ICTNI products is constant, the lifetime is usually more than 10 years and the share of manufacturing environmental impact will be relatively low even when low environmental impact electric power is used for the operation.

Enhanced meta-heuristic optimization of resource efficiency in multi-relay underground wireless sensor networks.

Achieving a balanced energy and spectral resource utilization is an interesting key design to extend the lifetime of underground wireless sensor networks (UWSNs) where sensor nodes are equipped with small limited energy batteries and communicate through a challenging soil environment. In this article, we apply an improved meta-heuristic algorithm, based on the Salp Swarm Algorithm (SSA), for multi-relay UWSNs where cooperative relay nodes amplify and forward sensed data, received from the buried source nodes, to the aboveground base station. Hence, the optimal nodes transmission powers, maximizing the network resource efficiency, are obtained and used to select beneficial relay nodes. The algorithm enhances the standard SSA by considering the chaotic map for salps population initialization and the uniform crossover technique for salps positions updates. Simulation results show that the proposed algorithm significantly outperforms the SSA in resource efficiency optimization and network lifetime extension. The obtained gain increases when the number of cooperative relay nodes increases. Furthermore, simulations prove the efficiency of the proposed algorithm against other meta-heuristic algorithms.

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.

High-efficiency and stable short-delayed fluorescence emitters with hybrid long- and short-range charge-transfer excitations

The pursuit of ideal short-delayed thermally activated delayed fluorescence (TADF) emitters is hampered by the mutual exclusion of a small singlet-triplet energy gap (ΔEST) and a large oscillator strength (f). Here, by attaching an multiresonance-acceptor onto a sterically-uncrowded donor, we report TADF emitters bearing hybrid electronic excitations with a main donor-to-acceptor long-range (LR) and an auxiliary bridge-phenyl short-range (SR) charge-transfer characters, balancing a small ΔEST and a large f. Moreover, the incorporation of dual equivalent multiresonance-acceptors is found to double the f value without affecting the ΔEST. A large radiative decay rate over an order of magnitude higher than the intersystem crossing (ISC) rate, and a decent reverse ISC rate of >106 s−1 are simultaneously obtained in one emitter, leading to a short delayed-lifetime of ~0.88 μs. The corresponding organic light-emitting diode exhibits a record-high maximum external quantum efficiency of 40.4% with alleviated efficiency roll-off and extended lifetime.

Modelling Carbon Storage Dynamics of Wood Products with the HWP-RIAL Model—Projection of Particleboard End-of-Life Emissions under Different Climate Mitigation Measures

Harvested wood products (HWPs) store a significant amount of carbon, and their lifetime extension and appropriate waste management, recycling, and reuse can contribute remarkably to the achievement of climate goals. In this study, we examined the carbon storage and CO2 and CH4 emissions under different scenarios of 200,000 m3 particleboard manufactured in 2020 by a hypothetical manufacturer. The scope of our investigation was to model the effects of a changing product lifetime, recycling rates and waste management practices on the duration of the carbon storage in wood panels and on their emission patterns. The aim of the investigation was to identify the most climate-friendly practices and find the combination of measures related to HWP production and waste management with the highest climate mitigation effect. We used the newly developed HWP-RIAL (recycling, incineration and landfill) model for the projections, which is a combination of two IPCC models parametrized for Hungarian circumstances and supplemented with a self-developed recycling and waste-route-selection submodule. The model runs covered the period 2020–2130. According to the results, the combined scenario with bundled mitigation activities had the largest mitigation potential in the modelled period, resulting in 32% emission reduction by 2050 as compared to the business-as-usual scenario. Amongst individual mitigation activities, increased recycling rates had the largest mitigation effect. The lifetime extension of particleboard can be a complementary measure to support climate mitigation efforts, along with the concept of cascade use and that of circular bioeconomy. Results showed that landfilled wood waste is a significant source of CH4 emissions on the long term; thus, incineration of wood waste is preferable to landfilling.

Battery Lifetime Extension in a Stand-Alone Microgrid With Flexible Power Point Tracking of Photovoltaic System

In stand-alone dc microgrids (dcMGs), battery energy storage systems (BESSs) are conventionally used for regulating the dc-link voltage, causing a continuous battery operation. Though operating the photovoltaic (PV) system at its maximum power point (MPP) yields minimum battery discharge current, the opposite is true for battery charging current. Therefore, reducing the battery charging current based on its state-of-charge (SoC) and the amount of available PV surplus power (which can be treated as virtually stored energy) is an opportunity for improving the battery life. The main objective of the control strategy proposed in this article is to prolong the battery lifetime by reducing the charging current and keeping the battery SoC at lower values if the PV power is enough to supply the loads. Additionally, the PV system is used as the primary asset to regulate the microgrid voltage. The dynamic performance of the proposed control strategy is validated with experimental tests under various operating conditions. Furthermore, its effectiveness in prolonging the battery lifetime is evaluated using an aging model of a lithium-ion (Li-ion) battery (without loss of generality) by simulated case studies.

Ultrathin, High-Lifetime Silicon Nitride Membranes for Nanopore Sensing.

Thin membranes are highly sought-after for nanopore-based single-molecule sensing, and fabrication of such membranes becomes challenging in the ≲10 nm thickness regime where a plethora of useful molecule information can be acquired by nanopore sensing. In this work, we present a scalable and controllable method to fabricate silicon nitride (SixNy) membranes with effective thickness down to ∼1.5 nm using standard silicon processing and chemical etching using hydrofluoric acid (HF). Nanopores were fabricated using the controlled breakdown method with estimated pore diameters down to ∼1.8 nm yielding events >500,000 and >1,800,000 from dsDNA and bovine serum albumin (BSA) protein, respectively, demonstrating the high-performance and extended lifetime of the pores fabricated through our membranes. We used two different compositions of SixNy for membrane fabrication (near-stoichiometric and silicon-rich SixNy) and compared them against commercial membranes. The final thicknesses of the membranes were measured using ellipsometry and were in good agreement with the values calculated from the bulk etch rates and DNA translocation characteristics. The stoichiometry and the density of the membrane layers were characterized with Rutherford backscattering spectrometry while the nanopores were characterized using pH-conductance, conductivity-conductance, and power spectral density (PSD) graphs.

Relieving Compression-Induced Local Wear on Non-Volatile Memory Block via Sliding Writes

Due to its non-volatility and large capacity, NVM devices gradually take place at various levels of memories. However, their limited endurance is still a big concern for large-scale data centres. Compression algorithms have been used to save NVM space and enhance the efficiency of those lifetime extension methods. However, their own influence on the NVM lifetime is not clear. In order to fully investigate the impact of compression on NVM, this paper first studies bit flips involved in several typical compression algorithms. It is found that more bit flips would happen in the shrunken area of a memory block. This induces the phenomenon of intra-block wear unevenness, which sacrifices NVM lifetime. We propose a new metric called local bit flips to describe this phenomenon. In order to relieve the intra-block wear unevenness caused by compression, this paper proposes a sliding write method named SlidW to distribute the compressed data across the whole memory block. We first divide the memory block into several areas, and then consider five cases about the relationship between new data size and left space. Then, we place the new data according to the case. Comprehensive experimental results show that SlidW can efficiently balance wear and enhance NVM lifetime.

Common DC-Link Capacitor Harmonic Current Minimization for Cascaded Converters by Optimized Phase-Shift Modulation

This paper investigates the influence of a constant carrier phase shift on the DC-link capacitor harmonic current of cascaded converters used in fuel-cell and mild-hybrid electric vehicles. In these applications, a DC-DC converter can be adopted between the battery and the motor drive inverter in a cascaded structure, where the two converters share the same DC-link. Since the DC-link capacitor of such a system represents a critical component, the optimization of the converter operation to limit the current stress and extend the lifetime of the capacitor is an primary objective. This paper proposes the use of a carrier phase shift between the modulations of the two converters in order to minimize the harmonic current of the DC-link capacitor. By harmonic analysis, an optimal carrier phase shift can be derived depending on the converter configuration. Analytical results are presented and validated by hardware-in-the-loop experiments. The findings show that the pulse width modulation carrier phase shift between the interleaved boost converter and the voltage source motor drive inverter has a significant influence on the DC-link capacitor current and thus on its lifetime. A case study with two-cell and three-cell interleaved boost converters shows a possible DC-link capacitor lifetime extension of up to 390%.

Ru Monoimines with Extended Excited-State Lifetimes and Geometrical Modulation of Photoinduced Mixed-Valence Interactions.

The photophysical properties of monodentate-imine ruthenium complexes do not usually fulfil the requirements for supramolecular solar energy conversion schemes. Their short excited-state lifetimes, like the 5.2 ps metal-to-ligand charge transfer (MLCT) lifetime of [Ru(py)4Cl(L)]+ with L = pz (pyrazine), preclude bimolecular or long-range photoinduced energy or electron transfer reactions. Here, we explore two strategies to extend the excited-state lifetime, based on the chemical modification of the distal N atom of pyrazine. On one hand, we used L = pzH+, where protonation stabilized MLCT states, rendering thermal population of MC states less favorable. On the other hand, we prepared a symmetric bimetallic arrangement in which L = {(μ-pz)Ru(py)4Cl} to enable hole delocalization via photoinduced mixed-valence interactions. A lifetime extension of 2 orders of magnitude is accomplished, with charge transfer excited states living 580 ps and 1.6 ns, respectively, reaching compatibility with bimolecular or long-range photoinduced reactivity. These results are similar to those obtained with Ru pentaammine analogues, suggesting that the strategy employed is of general applicability. In this context, the photoinduced mixed-valence properties of the charge transfer excited states are analyzed and compared with those of different analogues of the Creutz-Taube ion, demonstrating a geometrical modulation of the photoinduced mixed-valence properties.

Long-Term Performance of Ultrafiltration Membranes: Corrosion Fouling Aspect

The past decade has seen a rise in the importance of the ultrafiltration (UF) technique in the separation of various complex solutions. However, the fouling phenomenon is the main limitation to faster process development. To the best of the authors' knowledge, the present paper is the first to aim to identify the role of corrosion fouling in long-term UF. For this purpose, polyvinylidene fluoride (PVDF) and polyethersulfone (PES) membranes were used. The investigations were carried out with the use of both pilot-scale and laboratory-scale units. Results obtained in the present study have clearly demonstrated that the oil concentration has a significant impact on the process performance. Indeed, it has been noted that a reduction in oil concentration from 160 to 100 mg/L resulted in an increase in the PVDF membrane flux from 57 to 77 L/m2h. In addition, it has been shown that the feed temperature has a significant influence on the UF performance. Importantly, it has been shown that corrosion fouling is of vital importance in UF membranes. Indeed, corrosion products such as iron oxides contaminated the membrane surface leading to an irreversible decrease in the UF process performance. In addition, it has been found that repeating the chemical cleaning of the membrane units significantly reduced the intensity of the fouling phenomenon. However, the complete elimination of its effects was not achieved. Therefore, it has been indicated that cleaning agents recommended by membrane manufacturers do not remove corrosion products deposited on the membrane surface. Undoubtedly, the obtained results can be used in the design of UF units leading to the extension of membrane installation lifetime.

Distributed energy management for underground engineering microgrid with reliable power supply

AbstractBattery energy storage system (BESS) is of great significance to ensure underground engineering (UE) microgrid to have reliable power supply. Distributed energy management is one of the solutions that can enhance the microgrid reliability by efficiently scheduling the distributed appliances (such as diesel generator, BESS) to accommodate various scenarios. A distributed energy management model is proposed, which can help in reliable power supply by prolonging the lifetime of BESS and reducing the load loss. Considering the different energy consumption needs and dispatching capabilities of three regions of the UE microgrid, the proposed energy management model distributed dispatches the three regions in UE microgrid. In addition, considering the relationship between the depth of discharge and lifetime, the proposed energy management model also contains the BESS lifetime extension model constructed with dynamic charge‐discharge rate and dynamic bidirectional AC/DC converter efficiency. Based on the deterministic optimisation method, the optimal solution of the proposed energy management model is obtained. The effectiveness of the proposed energy management model is validated under six scenarios (that is grid connected mode, off grid mode, partial interconnection mode, interconnection mode, and independent modes with and without power exchange). The simulation results demonstrate that compared with the conventional model, the proposed model can reduce the operation cost by 6.46% and the load loss rate by 0.747%, which helps to improve the reliability of UE microgrid.

Construction of an optical sensor for molybdenum determination based on a new ionophore immobilized on a polymer membrane

ObjectivesIn this study, a new optical chemical sensor to assess molybdenum ion by incorporation of 1-(2-benzothiazolylazo)-2-hydroxy-3-naphthoic acid (BTAHN), dibutylphthalate (DBP) and sodium tetraphenylborate (NaTPB) to the plasticized poly vinyl chloride (PVC) matrices were prepared. MethodsWhen DBP was added to the membrane, the ionophore's tendency to act as a chromoionophore was greatly increased. Great stability, reproducibility, extended life time, and respectable selectivity for Mo6+ ion assessment throughout a wide number of transition, lanthanides, and heavy metals were all advantages of the accomplished sensor. ResultsAt optimum compositions and investigational circumstances, the sensor response was linear cross range of 8.5 × 10−8 to 4.4 × 10−5 mol/L. Sensor detection and quantification limits realistic on the definition that the sample amount results in a signal equal to the blank signal plus three and ten times of its standard deviation were establish to be 2.5 × 10−8 and 8.3 × 10−8 mol/L. The sensor reaction time (characterized as the time it required for the absorbance value to reach 95 %) was 3.0–5.0 min. ConclusionsThe achieved optical sensor was successfully applied to assess Mo6+ ion content in water, food, plant, and environmental samples.

Lifetime extension of the high voltage asynchronous machine in relation to the voltage endurance test

The study aims to achieve a simple, reliable, and significant lifetime extension of the high-voltage asynchronous machine in relation to the voltage endurance test. To achieve this goal, the focus was on achieving longer-lasting and more stable insulation of the stator package of an asynchronous machine. Longer-lasting and more stable insulation of a stator is achieved by reinforcing the weak points on its prefabricated multiturn coils. These reinforcements were performed with standard insulating materials that are used for the production of the prefabricated multiturn coils (because there is no data regarding the long-term behavior of new materials that show some better properties in laboratories, but only during short-term tests). With such reinforced weak spots based on prefabricated models, they were made by the classical procedure with the use of standardized tools. To track the effects of the improvement of the insulation characteristics of a stator, an algorithm was developed based on the law of increasing probability and the determination of lifetime curves to the voltage endurance test. The lifetime curves were determined by the method of increasing voltage with the transformation of the obtained results to the corresponding results by the constant voltage method. The applied algorithm that was formed for this study, had been verified with statistical reliability of 95%. The combined measurement uncertainty of the measurement procedure was about 5%.

Damage localization using electromechanical impedance technique based on inverse implementation

Structural Health Monitoring (SHM) systems allow maintenance planning which reduces maintenance costs. These systems may also allow lifetime extension of structures which allows reduction in lifecycle costs of structures. As a result, SHM systems have been of interest to researchers in civil and mechanical engineering sectors. The SHM system should be ideally low cost, suitable for continuous monitoring, and able to detect small levels of damage. The sensitivity to small levels of damage is even more important for composite structures as composites have low damage tolerance. Electromechanical Impedance (EMI)-based techniques have been proposed due to their sensitivity to low levels of damage. Furthermore, due to their high frequency of operation they are immune to ambient noise. Most of the studies using the EMI technique were limited to damage detection only. Recently some studies have used a network of sensors for EMI measurements and used them for damage localization. This paper follows on this trend of using a network of sensors for damage localization using EMI technique. A novel inverse algorithm is proposed for the damage localization. For the inverse technique, an analytical model for the correlation of distance and angle with the damage index (DI) is developed. This model is then used to generate a database of the DIs for a large number of damage scenarios. The measured DIs from the structure are then compared with this database and the scenario with the least mean error in the DIs is the predicted damage scenario. The algorithm takes into consideration the modeling errors and the measurement errors through regularization and in turn allows more accurate damage localization. The method is applied on different damage scenarios on an unidirectional composite sample. Some sensitivity studies such as the performance of the method using different fits have been carried out. In addition, the accuracy of damage localization of the proposed technique has been compared to a localization technique found in literature. The results show that indeed the proposed algorithm works and improves the damage localization using the EMI technique.

Defect evolution of neutron irradiated ITER grade tungsten after annealing

The microstructural evolution of neutron irradiated tungsten (W) after annealing and its correlation with the corresponding mechanical properties provides valuable insight on the defect interactions and their annihilation processes. This would result in the identification of recovery mechanisms, leading to the design of healing processes and thus, enabling the lifetime extension of fusion reactor components. Within this framework, samples from ITER specification forged W bar were neutron irradiated to a dose of 0.2 displacements per atom (dpa) at 600 °C in the Belgian Material Test Reactor (BR2) and subsequently annealed at 800 and 1000 °C. The evolution of the irradiation induced defects after annealing has been assessed by transmission electron microscopy (TEM), positron annihilation lifetime spectroscopy and electrical resistivity and its effect on the mechanical properties are discussed in terms of Vickers hardness. Neutron irradiation results in the formation of dislocation loops and voids. TEM observations show an increase in the size of both defect types after post irradiation (PI) annealing at both temperatures, accompanied by an initial increase in their density after PI annealing at 800 °C, followed by a subsequent decrease after PI annealing at 1000 °C. The presence of TEM-irresolvable defects of both types is revealed in the as-irradiated state, which is evidenced by the evolution of Vickers hardness, resistivity and positron lifetimes and their correlation after the PI annealing. In the as-irradiated state, as well as after PI annealing at both temperatures, the hardening is dominated by voids.