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The main aim of the present study is to explore the use of synthetic ester fluid as a transformer insulant. For this, the performance of thermally aged synthetic ester is investigated using corona inception voltage (CIV) measurement, fluorescent analysis, and dielectric spectroscopic studies. Then a fuzzy model is introduced to correlate the outcome of these studies to predict the key performance index and lifetime estimation of insulation structures. CIV tests for the thermally aged ester fluid, under AC voltage show 53.2% and 34% reduction in inception values due to ageing time and ageing temperature respectively. Furthermore, the effect of magnetic field on the performance of thermally aged ester is also studied and a drastic reduction of 54.3% and 39.4% respectively in CIV is observed. Statistical studies also indicate accelerated degradation of the insulation performance under the influence of the magnetic field, showing high scatter in CIV data indicated by decreasing beta values. Other studies such as fluorescent spectroscopy depict progressive shifts in fluorescence maxima and a decrease in emission intensity with ageing. Dielectric spectroscopy results show a manifold increase in dissipation factor due to thermal ageing. A fuzzy monitoring tool uses spectral data as input and at the output indicates the level of deterioration. The Rule-base of the model is framed using dielectric study.

Statistical modeling and analysis of satellite failure is an effective way to master the satellite operating status, and the results can provide important theoretical basis for the performance improvement of satellite reliability. In view of the dual-period characteristics of satellite failure distribution, a 2-Weibull segmented model for statistical modeling of satellite failure has been proposed in this paper. In order to improve the robustness of the parameter estimation for 2-Weibull segmented model, a parameter estimation method for 2-Weibull segmented model based on least squares Hough transform algorithm is continued to be proposed in this paper. And the feasibility and effectiveness of the parameter estimation method are verified by simulation experiments. The 2-Weibull segmented model is used for statistical modeling of 1584 satellite failure samples. The results show that, compared with the traditional single Weibull distribution model, the 2-Weibull segmented model proposed in this paper improves the fitting accuracy of satellite failure distribution by 46.15%.

Inverters are a leading source of hardware failures and contribute to significant energy losses at photovoltaic (PV) sites. An understanding of failure modes within inverters requires evaluation of a dataset that captures insights from multiple characterization techniques (including field diagnostics, production data analysis, and current-voltage curves). One readily available dataset that can be leveraged to support such an evaluation are maintenance records, which are used to log all site-related technician activities, but vary in structuring of information. Using machine learning, this analysis evaluated a database of 55,000 maintenance records across 800+ sites to identify inverter-related records and consistently categorize them to gain insight into common failure modes within this critical asset. Communications, ground faults, heat management systems, and insulated gate bipolar transistors emerge as the most frequently discussed inverter subsystems. Further evaluation of these failure modes identified distinct variations in failure frequencies over time and across inverter types, with communication failures occurring more frequently in early years. Increased understanding of these failure patterns can inform ongoing PV system reliability activities, including simulation analyses, spare parts inventory management, cost estimates for operations and maintenance, and development of standards for inverter testing. Advanced implementations of machine learning techniques coupled with standardization of asset labels and descriptions can extend these insights into actionable information that can support development of algorithms for condition-based maintenance, which could further reduce failures and associated energy losses at PV sites.

This paper presents a modified Damage Equalization Method with statistical features for life estimation of dielectrics. The paper postulates damage as a random variable, which resulted in establishing a relationship between the Weibull scale, shape parameters and the endurance coefficient ‘n’ of inverse power law. By the modified DEM (m-DEM), for the first time, a range of values of n for each material is proposed, which is useful for design engineers. Until now, the endurance coefficient of inverse power law and strength constant were treated as constants. Here, it is shown that these coefficients do have statistical features or variations. Experiments are conducted on oil impregnated paper and LDPE samples using accelerated step-stresses for life estimation. The results of the estimation of endurance coefficient are compared with existing methods and reasonable conclusions are drawn in favor of the proposed method. [ABSTRACT FROM AUTHOR]

In smart grid communications, home area network (HAN) plays an important role in managing data transmission among communicating devices through a smart meter. Performance of the network depends on the efficiency of modulation schemes used in the communicating devices such as rectangular quadrature amplitude modulation (RQAM) and Gaussian minimum shift keying (GMSK). Saleh-Valenzuela (S-V) and Weibull fading channels are appropriate models for indoor communication channels. Average symbol error rate (ASER) and average channel capacity (ACC) performance of indoor dynamic HANs with communicating devices using RQAM and GMSK are analyzed for these channel models. Numerical results are presented to demonstrate the effect of traffic intensity, number of active devices in HAN, and the modulation types with parameters of practical interest. [ABSTRACT FROM AUTHOR]

The experimental time-dependent dielectric breakdown and ON voltage reliability of advanced FD-SOI Z2-FET memory cells are characterized for the first time. The front-gate stress time is shown to significantly modulate the ON voltage and, hence, the memory window. The Weibull slope, $\beta $ , indicating the device variability to breakdown, and the time to soft breakdown, $\alpha $ , present different trends depending on the cell geometry. This fact highlights the tradeoff between variability and reliability to account for in Z2-FET designs. [ABSTRACT FROM AUTHOR]

Reliability analysis of multicomponent repairable systems with dependent component failures is challenging for two reasons. First, the failure mechanism of one component may depend on other components when considering component failure dependence. Second, imperfect repair actions can have accumulated effects on the repaired components and these accumulated effects are difficult to measure. In this paper, we propose a parametric statistical model to capture the failure dependence information with general component repair actions. We apply the maximum likelihood method to estimate the model parameters by utilizing the historical failure data. Statistical hypothesis tests are developed to determine the dependence structure of the component failures based on the proposed reliability model. The proposed methodology is demonstrated by a simulation study and case studies of a car body assembly process and a forklift vehicle system. [ABSTRACT FROM PUBLISHER]

A novel approach for inspecting the condition of porcelain insulators based on statistical analysis of electromagnetic radiations of live insulators is proposed in this paper. Realistic replicas of punctured and contaminated insulators were created in the laboratory following IEC standards. These defective insulators were tested under high voltage stress while the electromagnetic radiations originated from the partial discharge activities on the insulators were captured using an electric field sensor. During the experiments, a multitude of tests were conducted and resulted in measuring and recording a total of 410,000 cycles of discharge activities. A feature extraction algorithm was developed to calculate the statistical features of the phase resolved interpretation of partial discharge pulses. The results of analyzing the extracted features from the radiated signature of defective insulators indicate that the scale and shape parameters of a two-sided Weibull distribution function, fit to the recorded measurements, entail distinct information about the source of discharges that can be used to identify the source of defects. Based on the library of features extracted from the recorded electromagnetic radiations, a support vector machine (SVM) classifier was developed which can successfully classify the radiation signature of punctured and contaminated insulators. [ABSTRACT FROM PUBLISHER]

This paper compares the application of the Weibull distribution and the Crow-AMSAA (C-A) model to the analysis of cable joint failures. The procedures on how to use the two models to analyze failure data and to predict the future number of failures have been described before the models are applied to a set of early failure data. The data, which include 16 failures and 1126 suspensions, were collected from a regional power-supply company in China. This paper proves that the Weibull distribution provides more reliable results in the analysis of early-failure data since it considers the time to failure of each event. Whilst the method is more straightforward and requires less information, applying the C-A model can yield confusing results if not handled carefully. When analyzing the events, using time as x-axis and using the cable joint population as an axis can complement each other. Separating those data into subsections and analyzing them independently can yield useful information. Recent failure data can better reflect the current state of cable joints. The results of this paper should help utility asset managers better analyze their past failure events. [ABSTRACT FROM PUBLISHER]

The role of microstructure and doping on the mechanical strength of microscale tension specimens of columnar grain and laminated polysilicon doped with different concentrations of phosphorus was investigated. The average tensile strengths of undoped columnar and laminated polysilicon specimens were 1.3 ± 0.1 and 2.45 ± 0.3 GPa, respectively. Heavy doping reduced the strength of columnar polysilicon specimens to 0.9 ± 0.1 GPa. On grounds of Weibull statistics, the experimental results from specimens with gauge sections of 1000 \mu \textm\times 100~\mu \textm\times 1~\mu \textm predicted quite well the tensile strength of specimens with gauge sections of 150 \mu \textm\times 3.75~\mu \textm\times 1~\mu \textm , and vice versa. The large difference in the mechanical strength between columnar and laminated polysilicon specimens was due to sidewall flaws in columnar polysilicon, which were introduced during reactive ion etching (RIE) and were further exacerbated by phosphorus doping. Removal of the large defect regions at the sidewalls of columnar polysilicon specimens via ion milling increased their tensile strength by 70%–100%, approaching the strength of laminated polysilicon, which implies that the two types of polysilicon films have comparable tensile strength. Measurements of the effective mode I critical stress intensity factor, K \mathbf {IC,eff} , also showed that all types of polysilicon films had comparable resistance to fracture. Therefore, additional processing steps to eliminate the edge flaws in RIE patterned devices could result in significantly stronger microelectromechanical system components fabricated by conventional columnar polysilicon films. [2014-0269] [ABSTRACT FROM PUBLISHER]

In this paper, a comprehensive methodology for the statistic of SRAM Vmin is presented. A plotting method for the linearization of the statistical distributions is proposed, and methodologies for size scaling and statistical extrapolations are developed. Many analogies to the established statistical framework for time-dependent dielectric breakdown are found. [ABSTRACT FROM PUBLISHER]

Many consumer products are designed and manufactured so that the probability of failure during the technological life of the product is small. Most product units in the field retire before they fail. Even though the number of failures of such products is small, there is still a need to model and predict field failures for purposes of risk assessment in applications that involve safety. Challenges in the modeling and prediction of failures arise because the retirement times are often unknown, few failures have been reported, and there are delays in field failure reporting. Motivated by an application to assess the risk of failure for a particular product, we develop a statistical prediction procedure that considers the impact of product retirements and reporting delays. Based on the developed method, we provide the point predictions for the cumulative number of reported failures over a future time period, and corresponding prediction intervals to quantify uncertainty. We also conduct sensitivity analysis to assess the effects of different assumptions on failure-time and retirement distributions. [ABSTRACT FROM PUBLISHER]

This paper presents mobile-to-mobile (M-to-M) channel measurements and models at 1.85 GHz in dense-scattering suburban areas. Three test scenarios were considered for different transmitter (Tx) and receiver (Rx) antenna placements. Scenario 1: inside-vehicle-to-inside-vehicle (IV2IV), where both Tx and Rx antennas were placed inside the test vehicles; Scenario 2: inside-vehicle-to-walk (IV2W), where the Tx antenna was placed inside the vehicle and the Rx antenna was inside the pocket or next to the face of the tester; and Scenario 3: walk-to-walk (W2W), where the Tx and Rx were moving at walking speeds, the Tx antenna was placed on a test cart, and the Rx was inside the pocket or next to the face of the tester. To mimic more typical M-to-M channels in practice, eight sub-scenarios were configured under the availability of the line-of-sight (LoS) between the Tx and Rx. Detailed channel models are proposed for path loss, shadowing, small scale, and multi-scale fading based on the collected measurements. The level crossing rate (LCR) and average fading duration (AFD) are studied from the measurements and compared with the theoretical expressions. [ABSTRACT FROM PUBLISHER]

Existing reliability models for repairable systems with a single component can be well applied for a range of repair actions from perfect repair to minimal repair. Establishing reliability models for multi-component repairable systems, however, is still a challenge problem when considering the dependency of component failures. This paper focuses on a special repair assumption, called partially perfect repair, for repairable systems with dependent component failures, where only the failed component is repaired to as good as new condition. A parametric reliability model is proposed to capture the statistical dependency among different component failures, in which the joint distribution of the latent component failure time is established using copula functions. The model parameters are estimated by using the maximum likelihood method, and the maximum likelihood function is calculated based on the conditional probability. Based on the proposed reliability model, statistical hypothesis testing procedures are developed to determine the dependency of component failures. The developed methods are illustrated with an application in a cylinder head assembling cell that consists of multiple stations. [ABSTRACT FROM AUTHOR]

This work seeks to demonstrate the technical feasibility of offshore wind projects by calculating the preliminary estimate of wind energy production in the Brazilian marine environment, through a simplified methodology based on currently available data in a case study performed with the application of wind turbines. The Exclusive Economic Zone of Brazil is about 3.6 million km?, an area that can be harnessed for offshore wind energy production. The case study was conducted in Itamarac? Island, Pernambuco state with the aim of supplying the local energy demands. An analysis was carried out on the local wind conditions through an ocean wind map measured at a height of 10 m, and therefore, the wind speed was extrapolated to 90 m using the logarithmic law. The Weibull frequency distribution and the annual energy production were calculated. The results presented showed that three wind turbines at a rated power of 3 MW, including a calculated annual average wind speed of 7.15 m/s would generate around 30,000 MWh/year, which would be sufficient to ensure energy throughout the year in Itamarac? Island. [ABSTRACT FROM PUBLISHER]

During the test of ITER conductors at nominal conditions, a degradation of the current sharing temperature (Tcs) has been observed after electromagnetic cyclic loading. Rather than focusing on the microscopic phenomena at the origin of the degradation, the degradation process has been studied from a statistical point of view, analysing the whole dataset of ITER conductors: average degradations have been calculated after various cycle numbers. Possible correlation with the strand critical current has also been analysed. In order to model the evolution of Tcs has been correlated with the reliability against cracks formation; the reliability is in turn defined according to a two parameters Weibull distribution. The validity of this approach has been tested with the so-called “Weibull plot”. The Weibull exponents were calculated for several ITER conductors and were found to be lower than one, indicating that the failure rate, which may be regarded as the formation rate of fractures in the filaments composing the strands, is decreasing with the number of cycles. [ABSTRACT FROM PUBLISHER]

Accelerated repeated-measures degradation tests (ARMDTs) take measurements of degradation or performance on a sample of units over time. In certain products, measurements are destructive, leading to accelerated destructive degradation test (ADDT) data. For example, the test of an adhesive bond needs to break the test specimen to measure the strength of the bond. Lognormal and Weibull distributions are often used to describe the distribution of product characteristics in life and degradation tests. When the distribution is misspecified, the lifetime quantile, often of interest to the practitioner, may differ significantly between these two distributions. In this study, under a specific ADDT, we investigate the bias and variance due to distribution misspecification. We suggest robust test plans under the criteria of minimizing the approximate mean square error. [ABSTRACT FROM PUBLISHER]

False alarms in active sonar systems arising from physical objects in the ocean (e.g., rocks, fish, or seaweed) are often called clutter. A variety of statistical models have been proposed for representing the sonar probability of false alarm (Pfa) in the presence of clutter, including the log-normal, generalized-Pareto, Weibull, and K distributions. However, owing to the potential sparseness of the clutter echoes within the analysis window, a mixture distribution comprising one of the clutter distributions and a Rayleigh-distributed envelope (i.e., an exponentially distributed intensity) to represent diffuse background scattering and noise is proposed. Parameter-estimation techniques based on the expectation–maximization (EM) algorithm are developed for mixtures containing the aforementioned clutter distributions. While the standard EM algorithm handles the mixture containing log-normal clutter, the EM-gradient algorithm, which combines the EM algorithm with a one-step Newton optimization, is necessary for the generalized-Pareto and Weibull cases. The mixture containing K-distributed clutter requires development of a variant of the EM algorithm exploiting method-of-moments parameter estimation. Evaluation of three midfrequency active-sonar data examples, spanning mildly to very heavy-tailed Pfa, illustrates that the mixture models provide a better fit than single-component models. As might be expected, inference on clutter-source scattering based on the shape parameter of the clutter distribution is shown to be less biased using the mixture model compared with a single-component distribution when the data contain both clutter echoes and diffuse background scattering or noise. [ABSTRACT FROM PUBLISHER]

We propose a reliability model for describing the lifetime of devices and materials working under variable stress (i.e., stresses which are a function of time). The model is based on a two-parameter Weibull distribution obtained by retaining the leading term from a series expansion of a general cumulative hazard function. The scale parameter is related to the real-stress time evolution by means of a differential equation which can be integrated. The paper shows that the solution of this differential equation approaches a well defined asymptotic behavior when the time approaches infinity. The proposed model may include the physics involved in the failure criterion, and hence it can be consistent with accelerated life, step-stress, and variable-stress tests. This important property is illustrated by using the proposed reliability model to build statistical distributions for the lifetime of aluminum-alloy electrical wire connections, and thin film cracking in plastic integrated circuits which are stressed by temperature cycling, and thermal shock testing. A final discussion studies how the model allows extending the applicability, for example, by including time and stress thresholds in the failure criterion. [ABSTRACT FROM AUTHOR]

Accelerated life tests (ALTs) are often used to make timely assessments of the lifetime distribution of materials and components. The goal of many ALTs is the estimation of a quantile of a log-location-scale failure time distribution. Much of the previous work on planning accelerated life tests has focused on deriving test-planning methods under a specific log-location-scale distribution. This paper presents a new approach for computing approximate large-sample variances of maximum likelihood estimators of a quantile of a general log-location-scale distribution with censoring, and time-varying stress. The approach is based on a cumulative exposure model. Using sample data from a published paper describing optimum ramp-stress test plans, we show that our approach and the one used in the previous work give the same variance-covariance matrix of the quantile estimator from the two different approaches. Then, as an application of this approach, we extend the previous work to a new optimum ramp-stress test plan obtained by simultaneously adjusting the ramp rate with the lower start level of stress. We find that the new optimum test plan can have a smaller variance than that of the optimum ramp-stress test plan previously obtained by adjusting only the ramp rate. We compare optimum ramp-stress test plans with the more commonly used constant-stress accelerated life test plans. We also conduct simulations to provide insight, and to check the adequacy of the large-sample approximate results obtained by the approach. [ABSTRACT FROM PUBLISHER]

A fatigue model to predict the number of cycles for crack initiation and crack growth rate in Sn4.0Ag0.5Cu solder joints used in plastic ball grid array packages when subjected to accelerated thermal cycling has been developed. In addition to the conventionally used damage metrics such as accumulated strain and accumulated work, the normal strain in the solder joints has also been taken into consideration for fatigue model development. Unlike traditional fatigue models, which equate the life of the package to the life of the critical solder joint, the fatigue life of the package has been estimated by factoring in the reliability and hence the fatigue life of all the solder joints in the package. Good agreement was observed between the estimated package fatigue life from the fatigue model and the fatigue life as determined from experiments [ABSTRACT FROM AUTHOR]

We derive new unified probability density function (pdf) formulas based on the generalized Laguerre polynomial series expansion that cover a wide range of small-scale fading distributions in wireless communications. The unified envelope pdf covers many known Laguerre polynomial-series-based pdf's and small-scale fading distributions, which include the multiple-waves-plus-diffuse-power (MWDP) fading, κ-μ, Nakagami-m, Rician (Nakagami-n), Nakagami-q (Hoyt), Rayleigh, Weibull, and α-μ (Stacy) distributions as special cases. We highlight that the unified pdf formulas are general and applicable to characterize the distribution of any random variable defined on the positive range. We then propose two truncated forms of the pdf and prove that the original pdf and both truncated forms satisfy the properties of a valid pdf. A new cumulative distribution function and a moment-generating function of this pdf are derived. We also analyze the truncation error for the case when only a finite number of terms are kept in the series expansion. [ABSTRACT FROM AUTHOR]

Stiction remains one of the chief reliability concerns for microelectromechanical systems (MEMS) devices. In this paper, we quantify and analyze the rate of accrual of stiction in a standard MEMS device under a set of controlled temperature and humidity splits. An accelerated aging system was employed to more rapidly induce stiction in the MEMS. Optical characterization techniques were used to study the progression of stiction. The stiction accrual was quantified in terms of stiction equivalent energy, which provides compensation for mechanical fatigue in the devices due to long periods of operation. The fastest accrual of stiction was seen in the 90 °C, 80% relative humidity (RH) split with approximately 80% of the MEMS elements failing within 4.4 × 109 cycles (10 h) with 2.7 × 10-14 Joules of Stiction Equivalent Energy while the 60 °C, 20% RH showed the least stiction accrual rate with less than 2% failure for 2.26 × 1012 cycles (1500 h). In general, the stiction was seen to increase with an increase in humidity while mechanical fatigue showed an increase with an increase in temperature. Atomic force microscopy topography imaging was used to assess physical wear at the contacting areas. The results revealed that there were not any discernable changes in the surface profile due to long periods of actuation. [ABSTRACT FROM AUTHOR]

This paper presents a comparison of using different statistical distribution functions to predict ball-grid-array (BGA) solder joint reliability. Four functions are evaluated: two-parameter Weibull, three-parameter Weibull, mixed two-parameter Weibull and Lognormal. Statistical analysis demonstrates that the most commonly used two-parameter Weibull function may not present the best fit to the failure data; three-parameter Weibull and mixed Weibull may be better options in some cases by examining failure data histogram, data fit goodness, and potential failure mechanism change. [ABSTRACT FROM AUTHOR]

Safe and reliable design of MEMS components requires a statistical description of the material properties that are associated with failure. To this end, a series of microscale tensile tests was performed on polysilicon MEMS structures fabricated using Sandia National Laboratories' SUMMiT V™ process. Tensile bars were fabricated from each of the four freestanding polysilicon layers, with gage lengths ranging from 30 to 3750 pm. A two-parameter Weibull distribution appeared to adequately characterize the observed tensile strength distributions. The strength distribution was found to be dependent on the length of the tensile structures, as expected by the Weibull size effect, and unexpectedly strongly dependent on the layer from which the tensile bar was constructed. Specifically, the topmost polysilicon layer in the deposition process (poly4) was more than twice the strength of the bottom freestanding polysilicon layer (poly1). The mechanistic source of this layer-dependent strength appears to originate, at least in part, from process-dependent surface roughness, although other factors such as layer-dependent variations in microstructure, residual stress, and doping are also considered. A fracture mechanics analysis of the strength distributions suggests that the size of the critical flaws is in the vicinity from 50 to 150 nm. Fractography revealed crack origins along the sidewalls, corners, and top surfaces. Weibull strength distributions were also established at elevated temperatures: 200, 400, 600, and 800 °C in air and nitrogen environments. These results revealed the onset of ductility and reduction in strength at elevated temperatures: at 600 °C strength was less than 40% of the room temperature value. Most of the strength was regained if the material was tested at room temperature after a high-temperature exposure. In the discussion, we briefly review concepts for incorporating these observed strength distributions into probabilistic safe design of MEMS components. [ABSTRACT FROM AUTHOR]

The main goal of this paper is to propose an approach to calculate heavy ion SEU cross sections. The starting point is the diffusion model theory, which allows the charges diffusion but does not account for electrical field in the device. This electrical field is not necessary known in the device and is difficult to be introduced simply in the calculations. For this reason, we have empirically modified the diffusion model to account for electrical field. With only one empirical parameter, our Monte Carlo simulations allow reproducing the Weibull curves obtained for several technologies. In the last section, we focus on sub-threshold events and emphasize that they are partly due to the Rutherford scattering. [ABSTRACT FROM AUTHOR]

Flip-chip plastic ball grid array (FC-PBGA) pack. ages are widely used in high performance components. However, its die back is normally under tensile stress at low temperatures. This paper presents a probabilistic mechanics approach to predict the die failure probability in the FC-PBGA qualification process. The methodology consists of three parts: i) die strength test using four- point bending (4PB) method, ii) the radius of curvature (ROC) measurement of the assembled FC-PBGA at room temperature, and iii) finite element method (FEM) stress analysis. In the first part, a specially modified three-parameter Welbull function is used to fit the 4PB die strength data. The three parameters of the Weibull distribution are used as the sole description of the cracking characteristics for a specific die process in the late analysis. In the second part, the measured ROC of FC-PBGA at room temperature is used as a calibration input to determine the effective stress-free temperature of the FC-PBGA. It is used to overcome the difficulty caused by process-induced residual stress and unknown material properties. This effective stress-free temperature can be used in the stress analysis in the third part of the mentioned methodology. In the third part, the FEM is used to calculate the die stress distribution under most critical stage of certain qualification process. The calculated stress distribution is combined with the Weibull distribution parameters of die strength test to predict the die failure percentage. [ABSTRACT FROM AUTHOR]

The IEEE 802.15.4 network standard is being used as a suitable solution for wireless sensor networks in many environments and areas of expertise. They differ from other types of wireless networks because of its specific features. This work intends to analyse the mobility impact on IEEE 802.15.4 networks. For this reason it was developed a simulation platform with the requirements necessary to evaluate and compare environments with and without mobility. The results show that the mobility of elements in the scenarios evaluated caused signal degradation at short distances, but improvement in the rate of transmission for distances between 30 and 40 meters, as well as at distances greater than 60 meters. This is due to the fact that at intermediate distances the network presents high rate of collisions, making the technique CSMA/CA improve network performance in environments with more variability of the signal. [ABSTRACT FROM PUBLISHER]