基于可靠度计算的飞机发电机健康状态评估

为对飞机发电机健康状态进行评估,以故障数据为定时截尾样本,对威布尔分布参数进行矩估计,建立能够表征发电机故障规律的威布尔可靠度计算模型,提出了通过计算可靠度以定量评估健康状态的方法。工程应用表明,威布尔分布可较好地表征飞机发电机的故障规律,健康状态评估方法易于实现,且可行、有效。     

小样本数据下继电保护装置可靠性的组合威布尔分布评估方法

面对继电保护装置失效数据缺乏的情况,提出了一种基于组合威布尔分布的继电保护装置可靠性评估方法。首先,利用平均秩次法估算二参数威布尔分布的参数值,得到继电保护装置的分布密度函数;其次,选取蒙特卡罗抽样得到的Bootstrap子样作为三参数威布尔分布的样本数据,并采用灰色估计法对继电保护装置可靠寿命进行参数估计。最后,通过实例计算与其他方法进行对比,证明了方法在对小样本数据下的继电保护装置进行可靠性参数估计时精度更高。     

威布尔分布下竞争性故障装备的可靠性分析

利用外场故障数据,对威布尔竞争性故障装备进行了可靠性分析。首先对外场故障数据进行处理和失效模式分析,分别为各部件建立威布尔分布模型,得到其形状参数和尺度参数。进而在竞争性故障下,得到装备的可靠度函数和失效率函数。最后给出了一个陀螺仪算例来说明该分析方法的有效性。研究表明,该分析方法更符合装备的故障规律。     

压电陀螺的可靠性研究

本文分析了压电陀螺的可靠性,报导了压电陀螺的失效机理、失效模式和失效分布的研究结果,以及恒应力寿命试验和加速寿命试验确定的威布尔分布参数;η=8,945小时,t_E=13,912小时,m=0.58;加速度系数τ=3.8。 提高压电陀螺的可靠性研究表明,元器件筛选和改进工艺能降低压电陀螺的失效率;压电陀螺进行早期失效筛选能提高可靠度。 单轴和三轴压电陀螺的MTBF下限分别为9,651小时和3,217小时。洲际导弹用单轴和三轴压电陀螺的可靠度分别为99.82％和99.46％     

一种新的两参数改进威布尔分布的图像特征

针对Almalki S J和Yuan J提出的具有单调、单峰和浴盆形失效率函数的五参数改进威布尔分布,首先,通过增加一个形状参数得到六参数改进威布尔分布;其次,对其参数进行简化得到两参数改进威布尔分布;最后,研究了该分布的基本性质,从理论上证明了该分布的密度函数、失效率函数和平均失效率函数的图像特征,以及k阶矩的存在性。     

基于BRM的白光OLED恒定与步进应力加速寿命试验研究

为了获得白光OLED的寿命信息,通过加大电流应力开展了二组恒定和一组步进应力相组合的加速寿命试验。采用威布尔函数描述白光OLED的寿命分布,利用双线性回归法(BRM)估计出威布尔参数,确定了加速寿命方程,对白光OLED寿命是否符合威布尔分布进行了Kolmogorov-Smirnov检验,并利用自行开发的寿命预测软件计算出平均寿命和中位寿命。数值结果表明,恒定步进应力加速寿命试验方案是切实可行的,白光OLED的寿命服从威布尔分布,寿命应力关系满足线性Arrhenius方程,精确计算的加速参数可实现在短时间内OLED寿命的预测。     

激光大气传输接收功率闪烁的概率分布特征

在大气激光通信、激光测距、激光制导等应用中,由于大气湍流引起的接收光功率起伏对其工作效果及稳定性都有很大的影响。通过多相屏傅里叶数值模拟方法模拟了准直高斯光束在湍流大气中的传输,在考虑孔径平均效应的基础下,比较了弱起伏条件、中等起伏条件和强起伏条件下对数正态分布、Gamma-Gamma分布、指数威布尔分布和威布尔分布对仿真数据的拟合,分析得到弱起伏条件到强起伏条件下激光大气传输接收功率闪烁的概率分布服从指数威布尔分布,且该分布具有概率密度函数和累积分布函数结构简单、参数可以由大气参数计算得到的优点,为提高激光大气传输应用技术的性能提供了参考。     

威布尔分布研究及其在断路器电寿命中的应用

断路器电寿命的检测在断路器可靠性测试中占有重要地位,大量实验数据表明断路器的失效分布符合威布尔分布。采用相关系数法估算威布尔分布的位置参数、形状参数、尺度参数,并利用MATLAB开发对威布尔参数估计和数据拟合的程序。最后,对断路器试验故障次数进行了计算分析与应用。     

用微机实现威布尔分布参数的双线性回归最小二乘估计

威布尔分布是可靠性分析中常用的一种分布,本文针对威布尔分布参数估计中传统的图估计法的弊端,阐述了用微机数值估计方法取代图估计法的可行性、必要性及其重要意义,根据双线性回归原理在微机上用Ｍａｔｌａｂ实现了威布尔分布参数的最小二乘估计。     

氦氖激光管的工作寿命特性的研究

本文在理论上从电子元器件的特征寿命η所服从的逆幂律，分析导出了描述氦氖激光管工作寿命的以时间ｔ为自变量的威布尔分布函数；用图估和最好线性无偏估计（ＢＬＵＥ）两种方法处理寿命试验数据，结果都证实了氦氖激光管的工作寿命（特征寿命）服从逆幂律；最后给出了这种氦氖激光管的逆幂律方程式。     

Bayesian Confidence Bounds for the Weibull Failure Model

The following bounds are derived for the Weibull failure model when the parameter is being characterized by the inverted gamma and uniform probability density functions (pdf); they are lower and upper Bayes-confidence bounds for the scale parameter and lower bounds for the reliability function. To illustrate the results a Monte Carlo simulation was performed to obtain 90% and 95% Bayes-confidence bounds for the scale parameter and lower limits for the corresponding reliability function of the Weibull failure distribution. The consequences that one encounters when the following ``wrong' priors have been chosen to characterize the random behavior of the scale parameter are investigated. The results are compared when the prior pdf of ? is uniform but inverted gamma was used, and vice versa.     

One method for interval estimation of Weibull shape parameter

For three appropriated values of the random variable t, the corresponding values of the confidence limits for the cumulative Weibull distribution F(t), with parameters: β, γ and η, were calculated. On the basis of the appropriated and calculated values, the interval estimation of the shape parameter β was computed. The practical application of this method is illustrated by two examples.     

Estimation of Reliability from Multiple Independent Grouped Censored Samples with Failure Times Known

Failure times of one type aircraft-engine component were recorded. In addition, life times are periodically recorded for unfailed engine components. The data are considered as multiple s-independent grouped censored samples with failure times known. The assumed failure model is the 2-parameter Weibull distribution. Maximum likelihood estimates are derived. The exponential model is used for comparison. Monte Carlo simulation is used to derive s-bias and mean square error of the estimates. The asymptotic covariance matrix was computed for the sampling conditions studied. The maximum likelihood estimates of the reliability were obtained as a function of component operating time since overhaul.     

Inference on Weibull Percentiles and Shape Parameter from Maximum Likelihood Estimates

Four functions of the maximum likelihood estimates of the Weibull shape parameter and any Weibull percentile are found. The sampling distributions are independent of the population parameters and depend only upon sample size and the degree of (Type II) censoring. These distributions, once determined by Monte Carlo methods, permit the testing of the following hypotheses: 1) that the Weibull shape parameter is equal to a specified value; 2) that a Weibull percentile is equal to a specified value; 3) that the shape parameters of two Weibull populations are equal; and 4) that a specified percentile of two Weibull populations are equal given that the shape parameters are. The OC curves of the various tests are shown to be readily computed. A by-product of the determination of the distribution of the four functions are the factors required for median unbiased estimation of 1) the Weibull shape parameter, 2) a Weibull percentile, 3) the ratio of shape parameters of two Weibull distributions, and 4) the ratio of a specified percentile of two Weibull distributions.     

An alternative degradation reliability modeling approach using maximum likelihood estimation

An alternative degradation reliability modeling approach is presented in this paper. This approach extends the graphical approach used by several authors by considering the natural ordering of performance degradation data using a truncated Weibull distribution. Maximum Likelihood Estimation is used to provide a one-step method to estimate the model's parameters. A closed form expression of the likelihood function is derived for a two-parameter truncated Weibull distribution with time-independent shape parameter. A semi-numerical method is presented for the truncated Weibull distribution with a time-dependent shape parameter. Numerical studies of generated data suggest that the proposed approach provides reasonable estimates even for small sample sizes. The analysis of fatigue data shows that the proposed approach yields a good match of the crack length mean value curve obtained using the path curve approach and better results than those obtained using the graphical approach.     

Limited failure-censored life test for the Weibull distribution

When the distribution of lifetimes is 2-parameter exponential, Balasooriya (1995) provided a failure-censored reliability sampling plan to save test time. This paper extends the Balasooriya sampling plan to the Weibull distribution and provides a limited failure-censored reliability sampling plan (LFCR) to do life testing when test facilities are scarce. The s-expected test time of the LFCR is computed, and the optimal stopping rule of LFCR corresponding to the shortest test time is established. The s-confidence intervals for the parameters are generated     

Effect of randomness of Cu-Sn intermetallic compound layerthickness on reliability of surface mount solder joints

A statistical reliability analysis on thermal fatigue lifetime of surface mount solder joints, considering randomness of Cu-Sn intermetallic compound (IMC) layer thickness, is presented. Based on published thermal fatigue life test data, the two-parameter Weibull distribution of the thermal fatigue lifetime for a fixed IMC layer thickness is found, and a K-S goodness-of-fit test is conducted to examine the goodness of fit of the assumed Weibull distribution. Then, the Weibull parameters as functions of IMC layer thickness are obtained. Considering the randomness of IMC layer thickness, the MTTF and reliability of surface mount solder joints on thermal cycles are analyzed. For surface mount solder joints formed under the same conditions and loaded during the same thermal cycling as stated in the publication, numerical results of the MTTF and reliability are presented. The results show that when the mean value of MC layer thickness is low (e.g., smaller than 1.5 μm), the effect of randomness of IMC layer thickness is significant; i.e., the MTTF has strong dependence on IMC layer thickness distribution; and the reliability is significantly different at high thermal cycles. When the mean value of IMC layer thickness is high (e.g., greater than 2.0 μm), the effect of randomness of IMC layer thickness is negligible. Therefore, the presented results are important to the reliability study of surface mount solder joints. Even though the validity of the presented results based on the test data remains to be verified from other sources of data, the proposed statistical method is generally applicable for thermal fatigue reliability analysis of surface mount solder joints. By combining the proposed method with the forming mechanism of IMC layer under varying manufacturing and loading conditions, a comprehensive reliability analysis on thermal fatigue lifetime of surface mount solder joints can be expected     

基于LSSVM的威布尔分布形状参数估计

固态介质击穿寿命特性通常用威布尔分布来描述,形状参数卢反应了固态介质的失效特征,因而需要精确估计β值.提出了在小样本情况下基于最小二乘支持向量机(LSSVM)的参数评估方法,并给出了LSSVM在MOS电容与时间有关的击穿寿命分布评估中的应用实例,并与常规的最小二乘评估方法相比,得到的结果表明LSSVM的评估精度更高(均方误差更小)、鲁棒性更好,在小样本情况下能更精确地确定威布尔分布的形状参数.     

A Bayesian estimate of reliability in the Weibull distribution

A two parameter Weibull distribution is assumed to be the appropriate model of an engineering device. A Bayesian estimate of reliability is developed by assuming that a value β₀ of the shape parameter is known. Then we transform the Weibull distribution to the equivalent Exponential distribution by the transformation t′ = t^β0, so that techniques of analysis for the case of an exponential model can be applied to the transformed Weibull distribution. Then we can get the Bayesian estimate of reliability for this exponential distribution using a suitable loss function.     

A general Weibull model for reliability analysis under different failure Criteria-application on anisotropic conductive adhesive joining technology

In this paper, a generic four-parameter model has been developed and applied to the anisotropic conductive adhesive (ACA) flip-chip joining technology for electronics packaging applications. The model can also be used to predict any minimum failure cycles if the maximum acceptable failure criterion (in this case, a preset electrical resistance value) is set. The original reliability testing from which the test data was obtained was carried out on flip-chip anisotropically conductive adhesive joints on an FR-4 substrate. In the study, nine types of ACA and one nonconductive film (NCF) were used. In total, nearly 1000 single joints were subjected to reliability tests in terms of temperature cycling between -40/spl deg/C and 125/spl deg/C with a dwell time of 15 min and a ramp rate of 110/spl deg/C/min. The reliability was characterized by single contact resistance measured using the four-probe method during temperature cycling testing up to 3000 cycles. A single Weibull model is used for two failure definitions defined as larger than 50 m/spl Omega/ and larger than 100 m/spl Omega/ respectively using the in situ electrical resistance measurement technique. The failure criteria are incorporated into this Weibull model. This paper shows the flexibility and usefulness of Weibull distribution in this type of applications.