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To reveal the effects of aging state on the low-cycle fatigue (LCF) performance of 2024 Al alloy, LCF experiments were conducted on the 2024 Al alloy with three aging states (underaged (UA), peak-aging (PA) and overaged (OA)), respectively. It is found that under the total strain amplitude and plastic strain amplitude control, the Al alloy at UA and OA states exhibits higher LCF lives than that at PA state, respectively. For a more comprehensive evaluation, a hysteretic energy model with W0 as the fatigue damage capacity and β as the fatigue damage resisting exponent was used, which also shows the advantages of the OA states. This is because although the OA state has lower fatigue damage capacity W0 for the inferior strength-plasticity combination compared to the UA state, it has higher fatigue damage resistance exponent β because the obvious wavy slip manner of dislocations is conducive to strain homogenization, which is more important for increasing the fatigue life. Therefore, this study gives a comprehensive evaluation and revelation on the effects of aging state on the LCF properties of 2024 alloy.

The insulation performance of oil-immersed paper bushings is prone to deteriorate, primarily due to moisture intrusion and thermal aging. The frequency domain spectroscopy (FDS) method is commonly employed to assess the insulation condition of the bushing. However, identifying and extracting relaxation polarization information from the low-frequency region of the FDS curve can be challenging, and there is little research about the condition evaluation under the combined effects of aging states and moisture content. To address this issue, this article uses the Taylor formula mathematical model to extract characteristic parameters from the dielectric modulus curve of OIP bushings and uses the KNN algorithm to achieve the evaluation of aging and moisture status. Then, the effectiveness and accuracy of the proposed method are validated on three field OIP bushings. The results demonstrate that the evaluation accuracy of the proposed method exceeds 83%, which has significant advantages compared to other classification algorithms. The innovation of this article lies in extracting new feature parameters and combining them with intelligent classification algorithms to evaluate the moisture and aging state of the bushing. [ABSTRACT FROM AUTHOR]

The insulation performance of oil-immersed paper bushings is prone to deteriorate, primarily due to moisture intrusion and thermal aging. The frequency domain spectroscopy (FDS) method is commonly employed to assess the insulation condition of the bushing. However, identifying and extracting relaxation polarization information from the low-frequency region of the FDS curve can be challenging, and there is little research about the condition evaluation under the combined effects of aging states and moisture content. To address this issue, this article uses the Taylor formula mathematical model to extract characteristic parameters from the dielectric modulus curve of OIP bushings and uses the KNN algorithm to achieve the evaluation of aging and moisture status. Then, the effectiveness and accuracy of the proposed method are validated on three field OIP bushings. The results demonstrate that the evaluation accuracy of the proposed method exceeds 83%, which has significant advantages compared to other classification algorithms. The innovation of this article lies in extracting new feature parameters and combining them with intelligent classification algorithms to evaluate the moisture and aging state of the bushing.

Herein, the effect of the aging state on the impact toughness of three typical wrought Al alloys (7075, 2024, and 6A01) is investigated. At room temperature, the fracture mode of the three aluminum alloys at different aging states is a ductile transgranular fracture. At low temperatures, high‐strength aluminum alloys exhibit a mixture fracture of transgranular and intergranular, while medium‐strength aluminum alloys are still dominated by transgranular fractures. The effect of the aging state on the impact toughness of aluminum alloys was analyzed based on the deformation mechanism and morphology near grain boundaries. The underaged state with planar slip dislocations exhibits good plasticity and work‐hardening ability, which reduces the strain localization caused by dislocation plugging and thus improves the impact toughness of the alloy. Furthermore, the fine grain boundary precipitates and the narrow precipitation‐free zone of the underaged increase the uniform deformation capacity near the grain boundaries and inhibit the initiation and propagation of cracks. Compared with high‐strength aluminum alloys, medium‐strength aluminum alloys exhibit higher impact toughness due to the formation of a larger plastic zone and shear lip area during impact. [ABSTRACT FROM AUTHOR]

The dielectric voltage response characteristics of transformer oil–paper insulation are closely related to aging and moisture. Polarization voltage rate and degradation voltage rate can be used to evaluate insulation aging and moisture, respectively, but it takes a long time to acquire the above two characteristics. In this paper, the dielectric voltage response characteristic of transformer oil–paper insulation was measured by a single charge and multiple discharge method. The change rule of its initial slope characteristic was analyzed based on the relationship between the attenuation amplitude of dielectric polarization intensity reflected by the equivalent circuit and the initial slope of dielectric voltage response. The cumulative sum of initial slopes of dielectric voltage response (S) is proposed to evaluate the aging state of transformer oil–paper insulation. At the same time, the corresponding relationship between the characteristic quantity S and the content of furfural (Ck) in oil is studied experimentally. The results show that with the increase of insulation aging degree, both Ck and S increase. The fitting results show that the proposed characteristic quantity S and Ck have a linear relationship suitable for quantitative analysis of the insulation aging state. [ABSTRACT FROM AUTHOR]

Grain size and aging state are the two major microstructural factors affecting the mechanical properties of Al alloys. In this study, fatigue tests were conducted on 7075 Al alloy with varying grain sizes and aging states. The results indicate that both grain refinement and over aging (OA) treatment are beneficial for enhancing fatigue performance, with the 7075-Min alloy exhibiting the highest fatigue strength of 265.8MPa in the OA state. For grain size, a quantitative positive linear relationship was found between the reciprocal of the square root of the average grain size and the fatigue strength coefficient. Grain refinement optimizes the fatigue performance by increasing the fatigue strength coefficient. Compared to the under aging (UA) state, OA treatment promotes the growth and coarsening of precipitates at grain boundaries (GBs) and within the interior of grains. This change in precipitate morphology effectively facilitates dislocation cross slip, reducing fatigue damage caused by dislocation blocking. The impact of the precipitation-free zone (PFZ) on fatigue performance is negligible compared to that of the precipitates. This study clarifies the relationship between microstructure and fatigue performance, providing valuable insights for microstructure regulation to optimize the fatigue performance of Al alloys. [ABSTRACT FROM AUTHOR]

The high‐cycle fatigue (HCF) experiments were carried out for different aging states to study the effects of the aging state and yield strength on the fatigue properties of a 6A01 Al alloy. The results show that the 6A01 Al alloy with the highest yield strength at a peak‐aging (PA) state can exhibit the highest fatigue strength in comparison with the overaged (OA) state and the underaged (UA) state. The main reason is that the increased strength of the 6A01 Al alloy at the PA state can improve the plastic deformation resistance and inhibit the fatigue crack initiation. Additionally, the UA has a similar yield strength but a higher fatigue strength compared with the OA, which shows that the aging state also has a significant influence on the fatigue properties. Finally, combined with the previous studies on the 2XXX and 7XXX Al alloys, the effects of the aging state and yield strength on the fatigue properties of Al alloys are summarized. [ABSTRACT FROM AUTHOR]

The insulating paper of the transformer is affected by many factors during the operation, meanwhile, the surface texture of the paper is easy to change. To explore the relationship between the aging state and surface texture change of insulating paper, firstly, the thermal aging experiment of insulating paper is carried out, and the insulating paper samples with different aging times are obtained. After then, the images of the aged insulating paper samples are collected and pre-processed. The pre-processing effect is verified by constructing and calculating the gray surface of the sample. Secondly, the texture features of the insulating paper image are extracted by box dimension and multifractal spectrum. Based on that, the extreme learning machine (ELM) is taken as the classification tool with texture features and aging time as the input and output, to train the algorithm and construct the corresponding relationship between the texture feature and the aging time. After then, the insulating paper with unknown aging time is predicted with a trained ELM algorithm. The numerical test results show that the texture features extracted from the fractal dimension of the micro image can effectively characterize the aging state of insulating paper, the average accuracy can reach 91.6%. It proves that the fractal dimension theory can be utilized for assessing the aging state of insulating paper for onsite applications. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Moisture content and aging of oil-paper insulation are two important factors that cause deterioration of the insulation performance of power transformers. The water molecules and aging products are polar, which affects the dielectric response characteristics of the insulation system. Currently, the dielectric response testing technology has realized non-destructive evaluation of the moisture content of transformer insulation. However, the changes in the dielectric response caused by aging products are easily concealed by the influence of moisture, which makes the diagnostic technology ineffective for use in the evaluation of the aging of the oil-paper system. In order to avoid drawback, a new method utilizing frequency domain dielectric spectroscopy (FDS) and the water balance characteristics of the oil-paper insulation is proposed in this paper to evaluate the aging state of oil-paper insulation. The aging of oil-paper insulation will affect the water balance between oil and paper. In this paper, the experimental studies have shown that the water distribution coefficient between oil and paper and the degree of polymerization (DP) of the insulating paper shows a significant linear relationship. Accordingly, in this paper, FDS curves were used to evaluate the moisture content in the insulating paper, oil samples were taken to measure the moisture content in oil, and then the ratio of moisture content in oil and paper were calculated as the aging characteristic parameter. The linear relationship between the characteristic parameter and DP was used to evaluate the aging state of oil-paper insulation. The feasibility of the proposed method is preliminarily verified using oil-paper insulation samples at different aging states and with different moisture levels in the laboratory.

The oil‐impregnated transformer is an important part of the power system. The ageing degree of the internal oil‐paper insulation determines the service life of the transformer. The low frequency of the frequency domain dielectric spectroscopy can effectively characterise the ageing degree of transformer oil‐paper insulation. For accurately and quantitatively evaluate the aging state of oil‐paper insulation of transformer, the physical process of low‐frequency electrode polarisation is theoretically analysed in this work. Considering the polarisation of the low‐frequency electrode, the theoretical expression of the dielectric response of the equivalent XY model of the transformer is obtained. Meanwhile, to verify the rationality of the theoretical expression, the accelerated thermal ageing test of the oil‐paper insulation samples were carried out under laboratory conditions. The DC conductivity, ion mobility and FDS tests of oil‐paper insulation samples were tested on ageing 5, 10 and 15 days, respectively. The test results were combined with the theoretical expression of the low‐frequency dielectric response. It is found that the difference between the calculated result and the measured result is small. Therefore, the theoretical expression of the transformer equivalent XY model can be applied to calculate the dielectric parameters of the oil‐paper insulation at low‐frequency. [ABSTRACT FROM AUTHOR]

• It is no distinct difference in the LCF property of 7075 at various aging states. • The soft orientation within the coarse grains is a cause of fatigue cracking. • For 7075, the effect of tensile property on LCF is greater than that of slip mode. To study the effect of the aging state on the low-cycle fatigue (LCF) performance of 7075 Al alloy, LCF experiments with different strain amplitudes (Δε/2 = 0.5%- Δε/2 = 0.9%) were conducted for underaged (UA), peak-aging (PA) and overaged (OA) states with similar tensile properties in this work. The effect of the aging state on the cyclic stress response behavior and the LCF lives of 7075 Al alloy was revealed by observing the dislocation configuration after LCF. The microcrack orientation on the surface of LCF samples was observed by the electron backscatter diffraction (EBSD) technique, and the results showed that the soft orientation inside the coarse grains was the main cause of fatigue cracking. Combined with the previous studies, we summarized the dominant factors for the LCF and high-cycle fatigue (HCF) properties of 7075 Al alloys at different aging states, i.e., the LCF properties were determined by tensile properties, while the HCF properties were dominated by dislocation slip mode. [ABSTRACT FROM AUTHOR]

The rheological characteristics of two base binders and fourteen modified binders produced with seven additives at three aging states were studied. The test results included viscosity, failure temperature, rutting resistance factor, phase angle, complex modulus, percentage recovery value, fatigue factor, stiffness and m-value. It can be concluded that a proper concentration of alternative additive could be used to effectively achieve PG 76-22 binders. In addition, the binders modified with two of three new polymers showed weak resistances to low temperatures. Furthermore, the recovery percentages of alternative binders were relatively correlated to their phase angles at the short aging states. Meanwhile, this study also indicated that both binder source and alternative type determined the rheological characteristics of their modified binders. [ABSTRACT FROM AUTHOR]

The life expectancy of a transformer is closely related to the condition of its oil-paper insulation. In the present study, oil impregnated pressboard samples with different aging states and water contents were prepared under controlled laboratory conditions to analyze the oil-paper insulation condition of the power transformer by the dielectric response method. Dielectric response measurements, i.e., polarization and depolarization currents (PDC) and frequency domain spectroscopy (FDS), were conducted on the pressboard samples at different temperatures. Results show that the dielectric responses of oil impregnated pressboards are highly sensitive to aging, water, and temperature, but the influence of the temperature on FDS can be effectively eliminated by using the master curve technique. Meanwhile, dielectric characteristic parameters, which are sensitive to aging state and water content, were extracted to form a fingerprint database to indicate the various states of the oil impregnated pressboard. A grey correlation diagnosis model was first introduced to assess the aging state and water content of oil-paper insulation. Finally, FDS measurements were performed on a field transformer to verify the effectiveness of the new evaluation technique proposed in this paper for the condition assessment of the transformer oil-paper insulation. [ABSTRACT FROM AUTHOR]

The application of reclaimed asphalt pavement (RAP) is very promising and the research activities focusing on this subject is numerous in recent year. However, how to increase the percentage of RAP in the surface layer mixtures of asphalt pavement and meet or exceed the standards is challenging to the state highway agencies in the USA. The objective of this study is to explore the rheological properties of the high percentage (up to 50%) of RAP binder with three base binders in terms of five RAP binder content, two RAP binder sources, one HMA and one warm mix additive (WMA) technologies at three aging states. The viscosity, failure temperature, rutting resistance, fatigue resistance of various asphalt binders were tested in this study. The results indicated that the combined binders after a short term aging and a long term aging procedures still satisfied the requirement of asphalt binder set by Superpave binder specifications. In addition, increasing the RAP binder concentration could improve the rutting resistance of asphalt binder but a reduction in the fatigue resistance was noticed. However, the WMA additive could offset these properties of combined binder. Moreover, the results indicated that the RAP source typically affected the performance properties of combined asphalt binder and should be investigated individually. [ABSTRACT FROM AUTHOR]

For the oil-impregnated power transformers in service, the condition of the main insulation system is very important. This article reports a non-destructive evaluation technique based on time-frequency domain dielectric characteristics. First, the polarization/depolarization current and frequency-domain spectroscopy were well measured under controlled laboratory conditions. Then, the recovery voltage curves and recovery voltage polarization spectroscopy were also obtained by using the conversion method between polarization/depolarization current and recovery voltage based on the extended Debye model. After that, the time-domain dielectric characteristics, which can represent oil-paper insulation aging, were extracted from the polarization/depolarization current curves, recovery voltage curves and recovery voltage polarization spectroscopy. In addition, the frequency-domain dielectric characteristics, which can represent the oil-paper insulation aging, were also proposed in terms of frequency domain spectroscopy. Finally, the change rules of time-frequency domain dielectric characteristics under different aging times were investigated in depth. Results show that the time-frequency domain dielectric characteristics are sensitive to the aging states of power transformers, which could be utilized to diagnose the aging state of oil-paper insulation in field power transformers. [ABSTRACT FROM PUBLISHER]

In order to distinguish the influences of moisture and aging on the frequency domain dielectric response of oil-paper insulation and better apply frequency domain spectroscopy (FDS) to assess the insulation condition of power transformers, the oil-paper insulation samples with different moisture contents and different aging states were prepared in the laboratory. The FDS of the samples were tested and a group of characteristic parameters were extracted from dissipation factor (tan?) curves which could be used to assess the moisture content and aging states of oil-paper insulation respectively. The quantitative relationship among characteristic parameters, degree of polymerization (DP) and moisture contents (Km.c) was accurately established. The observations show that the proposed characteristic parameters are sensitive to the moisture in 10-3-102Hz, while the aging states influence the characteristic parameters in 10-3-10-1Hz. Meanwhile, an exponential relationship equation which could be used to assess the oil-paper insulation condition was established among the characteristic parameters, DP and the moisture content. Finally, the evaluation technique proposed in this paper was used to diagnose the insulation condition of several field transformers in this way, and its validity was preliminary and reasonably verified. [ABSTRACT FROM AUTHOR]

• The effect of the aging state on the corrosion fatigue properties of Al alloy is related to the stress level. • Under high-stress range where fatigue damage dominates, the over aged state shows better corrosion fatigue performance. • Under low-stress range, the over aged state has lower corrosion fatigue lives for its facilitation on the pitting-induced cracking. The corrosion fatigue performance of Al alloy components is crucial for their engineering applications. This study focuses on the corrosion fatigue properties of 7075 Al alloys in three different aging states, i.e. over-aging (OA), peak-aging (PA) and under-aging (UA) states. The results show that the fatigue damage mechanism of the Al alloy is greatly affected by the stress level. In the high-stress region where the cyclic number is short, the fatigue damage is mainly caused by dislocations accumulation and stress concentration on the grain boundary. Compared with the UA state, the wave slip dislocations at the OA state are easy to accumulate and annihilate at the second phase boundaries, which reduces the fatigue damage degree at the grain boundaries. However, in the low-stress range where the cyclic number is large, the corrosion fatigue life of the Al alloy is mainly controlled by pitting-induced crack initiation. For the OA state, the spacing and size of the precipitated phase are large, so it is easy to trigger corrosive pitting, which reduces the corrosion fatigue performance of the alloy. [ABSTRACT FROM AUTHOR]

With the advancement of wind energy, solar energy, and other new energy industries, the demand for energy storage systems are worth increasing. Supercapacitors gradually stand out among many energy storage components due to their advantages of high power density, fast charging and discharging speed, and long life. Predicting the capacity of supercapacitors from historical data is a highly non-linear problem, subject to various external and environmental factors. In this work, we propose an optimized forecasting model-an extreme learning machine (ELM) model coupled with the heuristic Kalman filter (HKF) algorithm to forecast the capacity of supercapacitors. ELM is preferred over traditional neural networks mainly due to its fast computational speed, which allows efficient capacity forecasting in real-time. Our HKF-ELM model performed significantly better than other data-driven models models that are commonly used in forecasting life of supercapacitors. The performance of the proposed HKF-ELM model was also compared with traditional ELM, Kalman filtering model, ELM optimized by the particle swarm optimization (PSO-ELM) and Kalman filter extreme learning machine models (KA-ELM). Different performance metrics, i.e., Root Mean Squared Error (RMSE), Mean Square Error (MSE) and R2 determination coefficient were used for the comparison of the selected models. The aging life of supercapacitors in different environments were also performed using the proposed approach. The results revealed that the proposed approach is superior to traditional data-driven models in terms of prediction aging life of supercapacitors and it can be applied in real-time to predict state of health (SOH) based on the previous charge and discharge data of supercapacitors. In particular, considering RMSE of forecasting, the proposed HKF-ELM model performed 77.62% better than the traditional ELM model, 77.46% better than the PSO-ELM model, 87.40% better than the traditional Kalman filter model, 82.51% better than the KA-ELM model in forecasting aging life of supercapacitors. The novelty of the proposed approach lies in the way the fast computational speed of ELMs has been combined with the accuracy gained by tuning hyperparameters using HKF. Fewer setting parameters, lower time cost and higher prediction accuracy have been need in our methodology compared to available models. Our work presents an original way of performing aging life of supercapacitors forecasting in real-time in industry with highly accurate results which are much better than pre-existing life forecasting models. [Display omitted] • HKF-ELM model is proposed to predict the remaining useful life of supercapacitors. • Heuristic Kalman filtering algorithm can solve the square matrix singularity. • The RMSE of the supercapacitor aging state estimation is as low as e −5. • HKF-ELM model can ensure high prediction accuracy and realize fast operation. [ABSTRACT FROM AUTHOR]

• The overaged samples have the lowest tensile strength among the three aging states, but their fatigue strength is the highest. • Planar slip dislocations are less likely to annihilate by cross slip at the UA state, thus contributing to better work-hardening ability, resulting in better strength and plasticity. • Wave slip dislocations at the OA state are frequently annihilated on the second phase, so that the number of dislocations reaching and gathering at GBs is relatively low, which reduces the damage at GBs. The high-cycle fatigue (HCF) behaviors of wrought Al alloys are vitally important for their industrial application. To optimize the fatigue property of the wrought Al alloy, the effects of aging conditions on the fatigue properties of 7N01, 7075 and 2024 Al alloys were studied. The results show that the overaged samples have the lowest tensile strength among the three aging states, but their fatigue strength is the highest. Further investigations on the dislocation morphologies indicates that the dislocations are easy to accumulate and annihilate at the second phase boundaries for the overaged state, which reduces the fatigue damage degree at the grain boundaries. Besides, the discontinuous distribution of the grain boundary precipitates and the increased width of the precipitate-free zone also contributed to the improved fatigue property of the overaged state. Those results should be significantly important for the optimization of their fatigue properties and the industrial application of wrought Al alloys. [ABSTRACT FROM AUTHOR]

In this study, Sasobit, as an asphalt modifier, was blended into two base asphalts- Pen 60/80 asphalt and SBS modified asphalt. The additional content of Sasobit was 2%, 3%, 4% and 5% by mass of asphalt. The Rolling Thin Film Oven test (RTFO) and the Pressure Aging Vessel test (PAV) simulate the asphalt's short-term aging and long-term aging separately. Two sets of evaluating systems (Penetration-grade system and Performance-grade system) were conducted on the asphalt's properties in three different aging states (the original state, the short-term aging state, and the long-term aging state). The high temperature properties of asphalt improved, and the lower temperature properties of asphalt declined. The variation trends in the three different states were also expressed by using the linear regression. The durability of the asphalt was evaluated based on these aged trends. It was evident that the durability of asphalt binder was related not only to the additive content but also to the asphalt binder type and aging state. [ABSTRACT FROM AUTHOR]