Lifetime Estimation Research Articles

High angle mass flux of an electrospray plume

High-resolution mass flux measurements of an electrospray plume are reported at high (>30^{circ }) angles, which are relevant to direct impingement of downstream electrodes. Interrogation of the plume edge greatly reduces uncertainty in electrospray device lifetime estimation related to mass flux to electrode surfaces. An angularly-actuated Thermoelectric Quartz Crystal Microbalance (TQCM) provides resolution down to sim2 pg cm^{-2} s^{-1}, allowing the highest resolution mass flux measurements of an electrospray plume to be reported herein. In-situ microscopy of the electrospray meniscus revealed changes to the electrode lines-of-sight of approximately 2°–3° due to the increasing meniscus tip height with beam current. Using the TQCM measurements and previous QCM results, a data-driven model is proposed for estimating electrode impingement as a function of beam current and aperture line-of-sight, which quantitatively captures the rapid increase in mass flux at higher beam currents or at low angles. The results show it is possible to guarantee negligible electrode impingement within a specified range of throttle levels.

Failure modes analysis and reliability enhancement of wind turbines

AbstractThe transition of the global energy system to affordable, reliable and clean sources is an important target of several international climate change accords and conferences such as the United Nations Framework Convention on Climate Change (UNFCCC) and its Conferences of parties (COP), Kyoto protocol and the UN Sustainable Development Goals (SDGs). The wind power is at the heart of these energy systems transformation and climate change mitigation. Indeed, the global capacity of wind turbines has seen tremendous growth, especially, during the past two decades which has made wind energy the fastest growing renewable source in the world. Nevertheless, the problem of premature failures and low‐reliability level of wind turbines have been increasingly noticed. This paper presents a new systematic analytical approach for failure modes and reliability analysis of wind turbines. The approach is a combination of three aspects which are qualitative and quantitative analysis using the fault tree method, reliability assessment as well as lifetime estimation and enhancement. Firstly, the various failure modes are presented. Then, mathematical modeling and reliability evaluation have been developed and simulated. Afterward, the actions that can be considered to improve the reliability and, consequently, the lifetime of wind turbines have been presented and analyzed. The results of the developed approach revealed that major reliability improvements, failure rate reduction and lifetime extension can be achieved, leading to a better return on investment, reduced maintenance as well as a safer and more reliable clean energy production.

Uniform fatigue damage tolerance assessment for additively manufactured and cast Al-Si alloys: An elastic-plastic fracture mechanical approach

• Influence of additively manufacturing and casting on microstructure and porosity characteristics as well as quasi-static and cyclic stress-strain behavior of Al-Si alloys. • Evaluation of Murakami-Noguchi approach and Shiozawa approach for fatigue limit and lifetime estimation, however, both approaches are not sufficient for AM Al-Si alloys. • Linking J integral (elastic-plastic fracture mechanics) including cyclic stress-strain curve by means of morrow parameter (K’, n’), defect size and position, stress amplitude and stress ratio. • New approach enables a uniform fatigue damage tolerance assessment of fatigue lifetime and limit for additively manufactured alsi10mg alloy as well as die-cast and sand-cast alsi7mg alloy. Lightweight Al-Si alloys are used in the automotive and railway industry due to their excellent strength-to-weight ratio and near-net-shape manufacturing. In additive manufacturing and casting, the near-net-shape manufacturing results in a non-homogenous solidification and cooling of the parts, leading to significant local gradient in microstructural and defect features as well as deformation behavior. In this paper, a uniform damage tolerance assessment was developed based on fracture mechanical approaches of Murakami (√area) and Shiozawa for a reliable defect-based mechanical design of fatigue-loaded structures. The linear-elastic fracture mechanical (LEFM) approaches of Murakami and Shiozawa were used to calculate defect-based lifetime curves, where the cyclic stress intensity factor (ΔK) at the failure-initiating defect (√area) was used to describe the local stress concentration conditions, called K-N curves, instead of nominal stress-based S-N curves. The LEFM-based K-N curves did not allow to describe the fatigue behavior in terms of a unified fatigue design of AM and casting material. Therefore, the cyclic stress-strain (CSS) behavior was used for a plasticity-modification of the LEFM approach by calculating the effective cyclic J integral (ΔJ eff ) to plot J-based K-N curves, called Kj-N curves. This elastic-plastic fracture mechanical (EPFM) approach allowed a uniform fatigue damage tolerance (FDT) assessment of AM and cast Al-Si alloys for the HCF regime by FDT law and fatigue limit by FDT limit. Exemplarily, the FDT limit could be used to predict synthetic Haigh diagrams for specific AM and cast batches and derive process- and service-relevant knowledge on the effect of tensile or compressive mean stress.

Multi-photon time-of-flight MLEM application for the positronium imaging in J-PET

Abstract We develop a positronium imaging method for the Jagiellonian PET (J-PET) scanners based on the time-of-flight maximum likelihood expectation maximisation (TOF MLEM). The system matrix elements are calculated on-the-fly for the coincidences comprising two annihilation and one de-excitation photons that originate from the ortho-positronium (o-Ps) decay. Using the Geant4 library, a Monte Carlo simulation was conducted for four cylindrical 22Na sources of β+ decay with diverse o-Ps mean lifetimes, placed symmetrically inside the two JPET prototypes. The estimated time differences between the annihilation and the positron emission were aggregated into histograms (one per voxel), updated by the weights of the activities reconstructed by TOF MLEM. The simulations were restricted to include only the o-Ps decays into back-to-back photons, allowing a linear fitting model to be employed for the estimation of the mean lifetime from each histogram built in the log scale. To suppress the noise, the exclusion of voxels with activity below 2% – 10% of the peak was studied. The estimated o-Ps mean lifetimes were consistent with the simulation and distributed quasi -uniformly at high MLEM iterations. The proposed positronium imaging technique can be further upgraded to include various correction factors, as well as be modified according to realistic o-Ps decay models.

Fast and Robust Single-Exponential Decay Recovery From Noisy Fluorescence Lifetime Imaging.

Fluorescence lifetime imaging is a valuable technique for probing characteristics of wide ranging samples and sensing of the molecular environment. However, the desire to measure faster and reduce effects such as photo bleaching in optical photon-count measurements for lifetime estimation lead to inevitable effects of convolution with the instrument response functions and noise, causing a degradation of the lifetime accuracy and precision. To tackle the problem, this paper presents a robust and computationally efficient framework for recovering fluorophore sample decay from the histogram of photon-count arrivals modelled as a decaying single-exponential function. In the proposed approach, the temporal histogram data is first decomposed into multiple bins via an adaptive multi-bin signal representation. Then, at each level of the multi-resolution temporal space, decay information including both the amplitude and the lifetime of a single-exponential function is rapidly decoded based on a novel statistical estimator. Ultimately, a game-theoretic model consisting of two players in an "amplitude-lifetime" game is constructed to be able to robustly recover optimal fluorescence decay signal from a set of fused multi-bin estimates. In addition to theoretical demonstrations, the efficiency of the proposed framework is experimentally shown on both synthesised and real data in different imaging circumstances. On a challenging low photon-count regime, our approach achieves about 28% improvement in bias than the best competing method. On real images, the proposed method processes data on average around 63 times faster than the gold standard least squares fit. Implementation codes are available to researchers.

Design and Lifetime Estimation of Low-Power 6-Input Look-Up Table Used in Modern FPGA

Due to technological advancements and voltage scaling, leakage power has become an important concern in CMOS design. The implementation of a field-programmable gate array (FPGA) circuit utilizes a portion of the FPGA’s resources as compared to an application-specific integrated circuit (ASIC). Both the utilized and unutilized parts of the FPGA dissipate leakage power. In this work, two dynamic power gating techniques, PSG-1 and PSG-2, are proposed, which are able to reduce the leakage power of the 6-input look-up table (LUT) used in the Xilinx Spartan-6 series. The obtained results show that the proposed approaches PSG-1 and PSG-2 reduce average leakage power by 54.61% and 66.69%, respectively, at the expense of nominal area and delay overhead. The proposed method is also capable of lowering the average total power of the 6-input LUT. The suggested PSG-1 and PSG-2 approaches reduce average power by 53.75% and 60.83%, respectively. However, header-based power supply gating is extremely vulnerable to the negative-bias temperature instability (NBTI) aging effect and, due to this, the lifetime of the circuit is reduced considerably. Therefore, in this work, lifetime estimation-based analysis is performed by varying the stress probability of the sleep transistor. The results show that the LUT with PSG-1 and PSG-2 techniques has a lifetime of 4.55 years and 11.13 years, respectively. The stress time of the sleep transistor is 50% for the PSG-1 technique and 25% for the PSG-2 technique, respectively.

Reliability and lifetime estimation of bioregenerative life support system based on 370-day closed human experiment of lunar palace 1 and Monte Carlo simulation

It is extremely important to accurately estimate reliability and lifetime of Bioregenerative Life Support System (BLSS) for its proper design, building and operation. However, this problem remains unsolved due to data deficiency of long-period prototype experiments. In this paper, the first ground-based experimental prototype of BLSS in China, Lunar Palace 1 (LP1), was selected as representative to estimate the reliability and lifetime of BLSS, because the number and time of each unit failure of LP1 was accurately recorded during the 370-day closed human experiment of LP1. Based on these time-series data, failure number probability distribution function of each unit and overall LP1 were formulated through parameter estimation and composite probability distribution function derived from units’ series and parallel connection. Then, the influence of each unit failure on overall BLSS reliability and lifetime was determined correspondingly through sensitivity analysis and Monte Carlo simulations. Finally, the numerous pseudo-random numbers obeying the overall failure probability distribution function of LP1 were generated to estimate the reliability and lifetime of BLSS through maximum likelihood estimation and Monte Carlo simulations. The results demonstrate that the failure possibility of five units, water treatment unit, mineral element supply unit, LED light source unit, atmosphere management unit and temperature and humidity control unit have greater impact on reliability and lifetime of BLSS, and the mean lifetime of BLSS was 19112.37 days (about 52.4 years) with 95% confidence interval of [17367.11, 20672.68] days (about [47.58, 56.64] years) under normal operation and maintenance of BLSS. This research can lay a theoretical foundation for design, building and operation of BLSS with high reliability and long lifetime in the future.

Remaining useful life estimation for two-phase nonlinear degradation processes

Owing to state transformation, operation switching, and degradation mechanisms, the processes of some deteriorating products often exhibit multiphase features. Unlike the traditional single-phase degradation model, the multiphase degradation model must consider the change-point variability and the associated degradation state. Therefore, degradation modeling and remaining useful life (RUL) estimation of the multiphase nonlinear deteriorating system is more challenging. With this consideration, we formulated two multiphase nonlinear degradation models based on the widely used nonlinear Wiener process-based model. Then, by modeling the uncertainty of the degradation state at the change-point, we obtained the exact analytical solutions for the lifetime and RUL estimation based on the two-phase model under the concept of the first passage time. Furthermore, we extended the results of the two-phase model to a multiphase model, and then provided an iterative method for lifetime and RUL estimations. Finally, we presented numerical and practical examples to verify the feasibility of the proposed method.

Fast algorithm for time decay estimation with applications to electrostatic ion beam traps

The ability of peptide trapping in an electrostatic ion beam trap (EIBT) is used for the measurement of renin substrate lifetime dependence from the pressure. The time decay estimation is traditionally obtained by optimization of nonlinear curve-fitting in the least-squares sense. This paper presents a novel algorithm to address this problem, using a numerical differentiation method as the basis for lifetime estimation. Simulations results show that the proposed method provides results similar to those obtained with the classical approach, but is faster by about two orders of magnitude. An experimental result is detailed, which shows the adequacy of this algorithm for the real-life monitoring of decay measurements, not only for EIBT, but also for other processes such as luminescence where exponential decay is involved.

The in‐service fatigue fracture mechanisms for the I‐stage low‐pressure compressor disk of the aircraft engine D30KU‐154

AbstractThis paper contains the in‐service fatigue fracture analysis for the first stage low‐pressure compressor disk of the aircraft engines D30KU‐154. Based on the results of the fractographic investigation on collapsed compressor disks the fatigue crack initiation and propagation principles were established. It is shown that the crack initiation in the rim part of the compressor disk is due to a high frequency loading that leads to very high cycle fatigue fracture. The total fatigue lifetime of the compressor disk is determined by simultaneous action of low amplitude loading due to blades vibration, and high amplitude loading due to flight cycle (centrifugal forces). Study of in‐service fracture of the compressor disk was based on the evaluation of numerical simulations of the stress state in the damaged zone under corresponding loading conditions. The estimation of fatigue lifetime and crack path predictions were performed based on the multiregime fatigue fracture model developed by the authors.

Rapid Screening of Novel Electrolytes for High Calendar Lifetime Lithium-Ion Cells with Silicon-Based Anodes

While cycle-life parity between graphite and silicon (Si) based lithium-ion batteries (LIBs) is being reached, calendar lifetime of Si anodes remains disappointing compared to its graphite counterpart1. Silicon anode, owing to its intrinsic high (electro)chemical reactivity, exhibits poorly passivating solid electrolyte interphase (SEI) characteristics in common electrolyte formulations optimized for graphitic systems like LiPF6 salt in EC:EMC solvents. Rapid electrolyte screening for calendar lifetime optimization is essential for enabling silicon anodes, as standardized calendar lifetime estimation with the USABC open circuit voltage reference performance test (OCV-RPT) requires long-duration experiments (~years) for accuracy2. In this work, we perform calendar lifetime screening of novel electrolytes for Si anodes utilizing voltage-hold (V-hold) experiments. The V-hold protocol with shortened runtime (~weeks) affords faster testing as compared to the conventional OCV-RPT protocol. Composite silicon anodes with low (15 wt.% Si) and high contents of silicon (70 wt. %Si) are tested with fluorine-free electrolyte systems (e.g. LiBOB in EC:EMC) and EC free electrolytes (e.g. LiPF6 in FEC:EMC) respectively. Capacity during the V-hold has reversible anode lithiation and irreversible SEI growth contributions; consequently, a physics-based capacity deconvolution algorithm is devised to accurately split the parasitic currents for quantitative calendar lifetime estimation. The development of this synergistic experiment-modeling testing paradigm aids in the identification of electrolyte compositions that form stable, passivating SEI films on the silicon-based anodes.Figure 1 shows the voltage-hold cycle data for (a) fluorine-free and (b) fluorine-rich (right) electrolytes with 15% Si composite anodes collected in a 3-electrode cell. The corresponding normalized capacity and current profiles for 4.1V hold portion are shown in (c) and (d) respectively. Accurate deconvolution of irreversible capacity from the hold capacity is needed to obtain SEI stability information for calendar lifetime. 1McBrayer, J.D., Rodrigues, M.T.F., Schulze, M.C., Abraham, D.P., Apblett, C.A., Bloom, I., Carroll, G.M., Colclasure, A.M., Fang, C., Harrison, K.L. and Liu, G., 2021. Calendar aging of silicon-containing batteries. Nature Energy, 6(9), pp.866-872. 2U.S. Department of Energy Vehicle Technologies Program, United States Advanced Battery Consortium Battery Test Manual For Electric Vehicles, Revision 3.1, October 2020 http://www.uscar.org/guest/article_view.php?articles_id=86 Figure 1

Impact of Relaxation Time on the Accelerated Cycle Ageing Tests of Lithium-Ion Batteries

As lithium-ion batteries are becoming the energy storage technology of choice for transport electrification, the accurate estimation and prediction of their service life remains a critical aspect for their successful adoption and integration. The established methods of lifetime estimation employ battery degradation models along with accelerated ageing test data. Although accelerated methods have been widely used in the literature over the last decade, there are still some discrepancies regarding the testing methodology and parameters. Specifically, in cycle ageing experiments, the relaxation time between cycles is chosen arbitrarily and is typically kept short to enable higher cycle throughput. Although this parameter is considered to have minimal influence on the test results1, its impact on the ageing rate and cell cycle life has not been thoroughly investigated. Furthermore, previous studies demonstrated significant capacity recovery after prolonged rest periods (≥2 days)2, however, their contribution is usually considered only at the end of the cycling ageing test3.In this work, the impact of cycling relaxation and rest periods in cycling ageing tests is systematically investigated. Commercially available cylindrical lithium-ion cells were subjected to long-term cycling at 10ºC with different discharge relaxation times. During cycling, three rest periods, i.e., 1min, 10min and 60min were investigated for the discharge relaxation steps, while the charge relaxation time was kept constant for all the cells at 1min. The cells were cycled in the manufacturer’s full voltage window with 0.3C/1C charge/discharge current respectively, and three cells were used in each test case to ensure the reproducibility of the results. At regular intervals, reference performance tests (RPT) were performed at 25°C for cell characterisation. After 6 months of ageing, a rest period of 2 weeks was incorporated into the ageing test, in order to investigate the influence of reversible losses in the course of accelerated cycling. During the rest period the cells were fully discharged and remained stored in open-circuit condition at 10°C. An RPT was conducted prior to the start as well as at the end of this period, before the cycling ageing regime was restarted.The relative capacity fade and resistance increase for the different relaxation times after approximately 8 months of ageing are presented in Figure 1. As illustrated, there is a clear increasing trend between cell degradation and relaxation time, i.e., cells that are rested for 60min after discharge are exhibiting the fastest rate of capacity fade and resistance increase. This result is counter-intuitive, since the longer the relaxation period the less cycles are performed between successive RPTs. Furthermore, the rest period is spent at low SOC, minimising the calendar ageing contributions, which are already expected to be comparatively small, due to the sub-ambient test temperature (10ºC). This behaviour was investigated further through differential voltage analysis (DVA), which revealed that the degradation modes across the three test cases exhibited minor differences, with higher losses of active material observed for the cells cycled with 60min relaxation and higher degrees of lithium inhomogeneity observed for the cells cycled with short relaxation (1min, 10min). The intermediate rest period led to significant capacity recovery for all cells, which reached up to >10% of the apparent capacity fade measured prior to the cycling break in the short relaxation test cases. The resistance values however were not affected, remaining almost constant before and after the rest period. The reversible losses were attributed to the anode overhang, due to the very low storage SOC, and to the increase in homogeneity of lithium distribution due to the increase in the peak intensity of the DVA curves. The capacity recovered through these mechanisms was effectively utilised once the ageing cycles were restarted and the ageing rates of each test case remained consistent, indicating that the cycling break did not affect the cell ageing trajectory.The results of this work demonstrate the strong influence of relaxation time on the cycle life of lithium-ion cells, which are cycled in otherwise similar conditions. This issue, which has not been reported before, needs to be considered in the design and interpretation of accelerated ageing tests. Similarly, reversible capacity losses need to be accounted and quantified in order to avoid the underestimation of cell cycle life. M. Reichert, D. Andre, A. Rösmann, P. Janssen, H. G. Bremes, D. U. Sauer, S. Passerini, and M. Winter, Journal of Power Sources, 239 45-53 (2013). B. Epding, B. Rumberg, H. Jahnke, I. Stradtmann, and A. Kwade, Journal of Energy Storage, 22 249-256 (2019). M. Lewerenz, P. Dechent, and D. U. Sauer, Journal of Energy Storage, 21 680-690 (2019). Figure 1

Durability of EPDM geomembranes - Lifetime estimation by using high pressure autoclave test method

For determination of end of service life different accelerated ageing tests are available. However, ageing of modern polymers in conventional oven ageing tests takes many years. In high-pressure autoclave test (HPAT), thermo-oxidative ageing is caused by elevated temperature and by elevated oxygen availability. This results in significantly shorter test times of around 8 months. An EPDM geomembrane was submitted to thermo-oxidative ageing in high pressure autoclaves (HPA) at 3 temperatures (75 °C, 80 °C and 85 °C) and 3 elevated oxygen pressures (5 bar, 10 bar and 51 bar). During exposure in HPAT the oxidation progress was monitored via tensile tests and oxygen pressure measurements. Tensile strength decreases steadily with increasing exposure time, temperature and oxygen pressure. Based on 75% residual tensile strength as theoretical failure criteria and Arrhenius based 3D extrapolation model, time till failure for service temperature at atmospheric condition was calculated. As a result, service life of about 360 years at 40 °C and atmospheric pressure was estimated.

Lifetime estimation of IGBT module using square-wave loss discretization and power cycling test

Lifetime estimation of IGBT module using square-wave loss discretization and power cycling test

Lifetime Estimation and Optimal Maintenance Scheduling of Urban Oil-Immersed Distribution-Transformers Considering Weather-Dependent Intelligent Load Model and Unbalanced Loading

Electricity distribution companies are in-charge-of supplying stable electric energy to urban customers over a wide geographical area. In these distribution networks, large number of Distribution-Transformers (DTs) are installed on towers or in electric-rooms with the ratings below 1000 kVA, which are the most important assets of distribution companies. Periodic maintenance and test services are not economically feasible for all in-operation transformers. Hence, estimating the remaining useful life and scheduling the maintenance times of DTs are of great technical and economic importance. An analytical approach is presented in this paper for predicting lifetime of DTs based on degree of polymerization. An appropriate Machine-Learning (ML) algorithm trained by measured data is selected for forecasting driven load according to the ambient temperature and humidity and day-hour schedules. The relation of Hot-Spot-Temperature in IEC60076∼7 is modified based on the measured data for accounting unbalanced-loading. Neutral-current is predicted using a trained ML-model. Another approach is proposed for determining times of oil filtering services aiming to minimize the maintenance cost and maximizing the remaining life. The proposed lifetime estimation method is validated by comparing its results with the damaged DT data of a sample network chosen as the case studies for this research, i.e., Bushehr province, Iran.

Arrhenius plots for Li-ion battery ageing as a function of temperature, C-rate, and ageing state – An experimental study

We present an extensive analysis of Li-ion battery ageing via Arrhenius plots. The V-shaped Arrhenius plots show minima at an optimum temperature corresponding to the longest cycle-life. The V-shape of the Arrhenius plots signifies the crossover between the two dominating ageing mechanisms – solid electrolyte interphase (SEI) growth in the high temperature range and lithium deposition in the low temperature range. Subjects of our investigations are commercial 5 Ah high energy 21,700-type cells with LiNi0.90Co0.05Al0.05O2 + LiNiO2 (NCA + LNO) cathode and Si/graphite anode (∼3% Si) and 0.1 Ah lab-made pouch cells with LiNi1/3Mn1/3Co1/3O2 (NMC111) cathode and a graphite anode. The results of the Arrhenius plots are analysed in the context of C-rate, cell ageing, and electrode properties. We find that the crossover between the dominating ageing mechanism and hence the optimum operating temperature of the Li-ion cells depend on C-rate, anode coating thickness/particles sizes, the state of health, and the shape of the capacity fade curve. Considering the change of the dominant ageing mechanism can help designing battery systems with longer service life. Additionally, we show a lifetime estimation for temperature dependent cycling of batteries emphasizing the merit of Arrhenius plots in the context of battery cell ageing.

Effect of thermal loading definitions on the mission profile-based reliability evaluation of power devices in PV inverters

The long-term mission profile-based lifetime evaluation of a PV inverter plays an important role in the Design for Reliability approach to ensure the required reliability performance. In previous studies, different thermal loading definitions have been considered for the mission profile-based lifetime estimation of power devices. It may affect the reliability prediction result considerably but its impact has not yet been studied. In this paper, the effect of thermal loading definitions on the predicted reliability of power devices in a PV inverter is investigated. The thermal loadings and reliability of power devices of a single-phase five-level T-type inverter by considering four different thermal loading definitions are comparatively analyzed and further discussed. Finally, some guidelines for selecting the thermal loading definition are suggested.

Effect of severe thermo-oxidative aging on the mechanical behavior and fatigue durability of short glass fiber reinforced PA6/6.6

The work deals with the fatigue lifetime estimation of Short Fiber Reinforced Thermoplastics (SFRP), with a focus on conjugated effects of thermal aging. Two materials containing 35% (V35) and 50% (V50) weight ratio of short glass fibers were aged for 500 h at 200°C in air and compared to the same materials in a Dry-As-Molded (DAM) state. Monotonic and fatigue tests were performed in samples machined out of injected plates and cut along three different orientations to the injection one (0°, 45°, 90°) in order to capture the anisotropy of the skin-core microstructure, classical in injected SFRP.Monotonic tensile tests evidenced the stiffening and embrittlement of the Polyamide matrix reported in the literature, nevertheless with an acuity depending on the matrix ratio and fiber orientation. Stress-controlled fatigue tests were performed at constant amplitude, frequency (10 Hz), temperature (200°C) and stress ratio R = 0.1. The fatigue curves of V35 are more affected by aging than those of the V50 material. The combined results from the mean strain evolutions and SEM observations confirmed that the initiation approach for fatigue lifetime estimation was still valid in aged composites. Several fatigue criteria, among the most recently reported in the literature, were evaluated from this database. The effect of aging on the cyclic evolution of the different Fatigue Indicator Parameters (FIP) involved in the criteria was analyzed preliminarily. For the present fatigue conditions, the best criteria for unaged materials (i.e cyclic creep energy-based ones) were shown to still be the best for aged materials. Finally, the ability to predict fatigue lifetime for aged composites from the identification of the fatigue criterion in the unaged state was evaluated.

Lifetime Estimation and Orientation Effect Based on Long-Term Degradation Analysis of Thermoset and Thermoplastic Insulators.

Polymeric insulators have replaced ceramic insulators due to their obvious properties like low surface energy, which exhibits good hydrophobic performance, low weight, etc. However, electric utilities have concerns about their long-term performance. In that context, the long-term performance of two different types of polymeric insulators are investigated in this study: thermoset Silicone rubber (SiR) and thermoplastic elastomeric (TPE). Multi-stress aging was performed in the different orientations of both types of polymeric insulators. During multi-stress aging, insulators are exposed to varied loads in both vertical and horizontal orientations, simulating actual service environmental conditions. Experiments were done in a chamber where different types of stresses were simulated, which resembles the weathering conditions of Hattar, Pakistan, which is one of the most polluted industrial zones. Both insulators were stressed in a chamber under the designed weathering conditions for two years and six months at different orientations. Polymeric insulators made of SiR perform better in the vertical position than that in the horizontal position. Furthermore, the experimental results show that both materials are capable in a variety of situations. SiR, on the other hand, performed well due to its high hydrophobicity, which means it is less impacted by contaminants and hence has a longer life and higher service performance than TPE.

The proton beam window for China Spallation Neutron Source

The proton beam window is one of the key devices for China Spallation Neutron Source (CSNS), which is used to separate the high vacuum from the helium circumstance at the target station, as the interference of the accelerator and the target. The design of the proton beam window is a comprehensive issue, covering the beam scattering, energy deposition, thermal–mechanical analyses, remote maintenance and lifetime estimation. We have proposed a single–double layer structure according to the beam distribution of CSNS, which can decrease the beam scattering and energy deposition when the beam passing through, and fulfill the material properties well simultaneously. The proton beam window is connected to the accelerator and the helium vessel by inflatable seals, which has a leak rate as low as 3.9 × 10−10 Pa m3/s and can maintain the vacuum at accelerator side below 1 × 10−4 Pa level. The lifetime of the window is estimated as seven years based on helium production in the condition of the highest current density of 5.85 μA/cm2. The creep elongation is extrapolated only 0.83% in the lifetime, which is small and can be considered safe.