Two‐Stage Reliability Sampling Plans with Bogey Tests

This article considers the design of two‐stage reliability test plans. In the first stage, a bogey test was performed, which will allow the user to demonstrate reliability at a high confidence level. If the lots pass the bogey test, the reliability sampling test is applied to the lots in the second stage. The purpose of the proposed sampling plan was to test the mean time to failure of the product as well as the minimum reliability at bogey. Under the assumption that the lifetime distribution follows Weibull distribution and the shape parameter is known, the two‐stage reliability sampling plans with bogey tests are developed and the tables for users are constructed. An illustrative example is given, and the effects of errors in estimates of a Weibull shape parameter are investigated. A comparison of the proposed two‐stage test with corresponding bogey and one‐stage tests was also performed. Copyright © 2012 John Wiley & Sons, Ltd.     

Numerical study of compact shear (Mode II) type test specimen geometry

The Iosipescu shear test specimen geometry has been investigated by a number of research workers in recent years with conflicting results. The paper describes a numerical study of a compact shear test specimen, based on the Iosipescu geometry, which is proposed to investigate size effects in shear failure. A range of geometries has been studied and the extreme cases are reported. Results are presented for the largest absolute principal stresses together with a detailed study of the stresses between and around the roots of the two notches introduced in the test specimens. The results for the largest absolute principal stresses show that tensile stresses are created at the roots of the two notches. These tensile stresses may result in Mode I failure and probably account for the Mode I or mixed mode fracture observed in tests using the Iosipescu geometry. The results for the distribution of stresses between the roots of the two notches show that deep notches increase the likelihood of shear fracture prior to tensile failure. Shallow notches give a stress distribution similar to that developed in the indirect tensile test and hence tensile failure is likely to precede shear failure in such cases. Further numerical and experimental work is proposed.      

Goodness-of-fit tests for the inverse Gaussian and related distributions

In this paper, tests of goodness-of-fit for the inverse Gaussian distribution are developed. The distribution involves a shape parameter and, because of this, some test approaches lead to inconsistent strategies. A consistent test is proposed and its properties investigated. A table of critical points is provided and both the level and the power of the test are explored by simulation. It is seen that the test is more powerful than most of its competitors. The framework is widened to cover satellite distributions of the inverse Gaussian and some types of censored data. An example concludes the paper.     

The Difference Test Statistic for Two Suppliers with Linear Profiles

Comparing two suppliers for linear profiles is a very important task for supplier management. The difference test statistic based on the process‐yield index is proposed to tackle the better process selection for linear profiles. A simple form of the sampling distribution of the process‐yield index is derived by a simulation study. Therefore, the asymptotic normal distribution of the difference test statistic is established. The results provide useful information to practitioners. An example from the leather industry is presented to illustrate the applicability of the proposed method. Copyright © 2014 John Wiley & Sons, Ltd.     

Testing Normality in Designs With Many Parameters

Goodness-of-fit tests are proposed for the assumption of normality of random errors in experimental designs where the variance of the response may vary with the levels of the covariates. The exact distribution of standardized residuals is used to make the probability integral transform for use in tests based on the empirical distribution function. A different mean and variance is estimated for each level of the covariate; corresponding large sample theory is provided. The proposed tests are robust to a possible misspecification of the model and permit data collected from several similar experiments to be pooled to improve the power of the test.     

Early failure analysis of machining centers: a case study

To eliminate the early failures and improve the reliability, nine ex-factory machining centers are traced under field conditions in workshops. Their early failure information throughout the ex-factory run-in test is collected. The field early failure database is constructed based on the collection of field early failure data and the codification of data. Early failure mode and effects analysis is performed to indicate the weak subsystem of a machining center or the troublemaker. The distribution of the time between early failures is analyzed and the optimal ex-factory run-in test time for machining center that may expose sufficiently the early failures and cost minimum is discussed. Suggestions how to arrange ex-factory run-in test and how to take actions to reduce early failures for machining center is proposed.     

Sampling plans for vehicle component reliability verification

Today's vehicle customers' demand for better quality and reliability is increasing. A typical reliability requirement is that of a lower bound on product reliability at a pre‐specified design life target (called the ‘bogey’) with specified confidence. For the purpose of reliability verification, one way to verify conformance to the requirements is to perform a test and terminate it after running for a certain period of time, cycles or mileage and to make a decision according to the test criterion. The approach presented in this paper specifically addresses the means to design tests that satisfy these important requirements and objectives. All the mathematical derivations are primarily based on a component life distribution that is assumed to follow a Weibull distribution with an assumed value of the shape parameter. By the proposed approach, only the GEM table (derived from the exponential case) is required. The test engineer has the option of trading off between the quantity of samples and the test bogey ratio (the test length relative to the bogey) so as to meet the specific objectives under the constraints. Copyright © 1999 John Wiley & Sons, Ltd.     

Improved design of dust test chamber for uniform distribution of dust sedimentation rate

Soiling problems are always encountered for equipment installed in outdoor environments, such as headlamps of automobiles, air conditioners, solar collectors, and so on. How to prevent soiling problems on this equipment is one of the challenges for the design of their external layouts. Thus, evaluations of the dust sedimentation quantities on the surfaces of such equipment are necessary. Outdoor testing is usually straightforward but it takes a long time to experience various environmental parameters, such as dust-laden air, wind speed, wind direction, and so on. Indoor tests, performed in a dust test chamber, are instruments for controlling various environmental parameters independently. The conventional design for a dust test chamber is aimed at providing for a test under extreme environmental conditions. The uniformity of dust sedimentation rate within the chamber is not rigorously controlled. Nevertheless, some applications such as the effect of dust sedimentation on the glazing of solar collector require uniform distribution of dustfall in the test chamber for the indoor (laboratory) test. An improved design for a conventional dust test chamber is proposed. Performance tests done with the remodeled dust test chamber based on the improved design show that the normalized standard deviation of the dustfall concentration can be controlled within 2.41% ± 1.29%.     

Test method for enhanced mechanical shock fragility statistics accuracy

An optimum cushioning package, which is neither excessive nor inadequate, must be designed to ensure cushioning performance that maintains an acceptable failure rate during transportation while also minimizing packaging costs. For this purpose, statistics pertaining to transport hazards and product shock strength must be engaged. The proposed study presents a test method to enhance the statistical accuracy of mechanical shock fragility of products. Sample statistics are invariably unknown; hence, optimum test‐setting values cannot be determined at the beginning. The proposed test method has been devised for determining optimum test‐setting values of the (n + 1)th sample using statistics of n samples being tested. An improvement in the estimation accuracy of the variation coefficient for the critical‐velocity‐change test was confirmed via simulations performed using the proposed method. Optimization of the test‐setting value has also been experimentally confirmed. A comparison of histograms and statistics obtained using experimental results has demonstrated that the proposed method can better estimate distribution shapes compared with the simple method. An example of the application of experimental results to stress‐strength models has also been described. The observed result has a considerable influence on the design of cushioning packages, thereby demonstrating effectiveness of the proposed method.     

Some notes about nonparametric tests for the equality of two populations

A new nonparametric test for the equality of two populations is proposed. The test is a generalization of the Girone-Cifarelli test (see Girone 1964, and Cifarelli 1974, 1975) which has been shown to be occasionally more powerful than other nonparametric tests, such as the Kolmogorov-Smirnov test. The test is based on a measure of dissimilarity between the sequences of ranks corresponding to the samples drawn from the two populations. The test can be adapted to verify the hypothesis of equality against one-sided and two-sided alternatives. Exact and asymptotic critical values of the test are provided. The asymptotic distribution of the test-statistic underH _o shows an interesting link with Brownian motion in [0,1].     

带趋势项GARCH误差模型参数变化的残量检验

本文研究带趋势项GARCH误差模型的参数变点检验.在参数未知的情况下,利用残量累积和检验以消除相依序列对检验结果的影响:研究表明在原假设条件成立下,残量累积和统计量的极限分布是一个标准布朗桥的上确界.蒙特卡罗数值模拟和IBM收益率数据分析的结果都充分说明了本文方法的有效性和实用性.     

非线性振型结构HFFB试验模态力计算方法及不确定性分析

基于高频测力天平风洞试验对非线性振型结构的风致响应提出了改进的评估方法。假设结构风荷载沿高度的分布与阵风风压分布相同,采用结构真实振型计算风荷载模态力。推导了高耸结构风荷载模态力及风致响应计算公式,可以考虑结构多阶真实振型,从而使高频测力天平方法可更为准确地评估非线性振型结构的风致响应及等效静力风荷载。对某一质量、刚度有突变的高耸结构进行了高频测力天平风洞试验,与现有的线性化振型法进行对比,结果表明在弱非线性振型下,线性化振型法得到的加速度响应较层荷载假设方法偏大约40%。研究了层荷载分布的不确定性对计算加速度响应结果的影响,结果表明在阵风剖面层荷载的假设下,荷载分布的不确定性对结构最大加速度响应的影响很小,验证了本文方法的适用性。     

复合材料多钉连接钉载矢量传感器

在总结复合材料多钉连接钉载测试方法的基础上,针对单向载荷传感器应用中必须已知钉载方向且需要按照钉载方向装设传感器的缺点,提出了钉载矢量传感器方案。钉载矢量传感器无预设安装角度要求,能够测量载荷方向;并对钉载矢量传感器的选材、应变片方案及开槽尺寸进行了设计,制造了钉载矢量传感器。采用复合材料单钉单剪螺栓连接,分别对钉载矢量传感器测量结果的线性符合性、重复性、安装角度影响以及载荷方向测量能力进行了测试研究。测试结果表明:钉载矢量传感器满足工程上对载荷分配测试的技术要求,验证了本文所提出的钉载矢量传感器的适用性。     

Analysis of grouped data from field-failure reporting systems

Observed reliability data from fielded systems is highly desirable because they implicitly account for all actual usage and environmental stresses. Many companies and large organizations have instituted automated field-failure reporting systems to organize and disseminate these data. Despite these advantages, field data must be used with caution because they often lack sufficient detail. Specifically, the precise times-to-failure are often not recorded and only cumulative failure quantities and operating times are available. When only data of this type are available, it is difficult to determine whether component or system hazard function varies with time or is constant (i.e., exponential distribution). Analysts often use the exponential distribution to model time-to-failure because the distribution parameter can be estimated with just the merged data. However, this can be dangerous if the exponential distribution is not appropriate. An approach is presented in this paper for Type II censored data, with and without replacement, to evaluate this assumption even when individual times-to-failure are not available. A hypothesis test is presented to test the suitability of the exponential distribution for a particular data set composed of multiple merged data records. Two examples are presented to demonstrate the approach. The hypothesis test readily rejects an exponential distribution assumption when the data originate from a Weibull distribution. This is a very important result because it has generally been assumed that time-to-failure data were always required to evaluate the suitability of specific time-to-failure distributions.     

基于泊松过程的超高斯随机振动试验控制技术研究

针对工程化的超高斯随机振动试验控制技术实现尚存在问题,在对其控制原理研究的基础上,提出基于泊松过程的超高斯随机振动控制策略。利用参考谱设计出符合控制要求的滤波器,通过泊松过程产生泊松点,使泊松点的信号取值服从正态分布,利用该信号与滤波器之间的卷积运算产生用于系统控制的驱动信号,从而实现对超高斯随机振动试验控制系统的功率谱和峭度同时控制,且二者相互独立。仿真与实验结果表明,基于泊松过程的超高斯随机振动试验控制算法,其控制输出响应谱与参考谱的误差满足振动试验工程上±3dB要求,控制峭度也达到很高的精度,完全满足工程要求。     

基于ISTA测试的小型非易碎品包装方法的标准化研究

目的 对小型非易碎品在分拨中心的二次包装方法进行标准化研究,以应对物流中的过度包装问题.方法 在问卷调查与实地调研的基础上,统计分析包装材料使用数量和包装方法;并应用鱼骨图进行影响因素分析,提出小型非易碎品二次包装标准化方法;最后参照ISTA测试,进行振动测试、跌落测试,从而确定包装间隙率的阈值、充气袋放置数量、气泡膜全方位包裹圈数.结果 采用文中提出的标准化包装方法,能够在确保商品运输安全性的同时,节省充气袋使用量62.3％,气泡膜用量80.8％.结论 能有效解决小型非易碎品物流配送过程中的过度包装问题.     

电能表温度影响试验自动测试系统

电能表温度影响试验自动测试系统是运用计算机自动控制技术,对恒温恒湿室的温度进行自动控制,在恒温恒湿室的各个恒定温度点分别对被检电能表的误差进行自动检验,最终自动计算出电能表的基本误差随外界温度改变的变化率。自动测试系统不仅可以大大延长有效试验时间、提高设备使用率,还可以达到减少人工、减少人为差错的目的,更能提升整个温度影响试验过程的严谨性和规范性。在提出自动测试系统的总体设计要求后分别介绍了该系统的硬件和软件的技术方案。     

Multivariate statistical process control charts based on the approximate sequential χ2 test

Similar to the univariate CUSUM chart, a multivariate CUSUM (MCUSUM) chart can be designed to detect a particular size of the mean shift optimally based on the scheme of a sequential likelihood ratio test for the noncentrality parameter. However, in multivariate case, the probability ratio of a sequential test is intractable mathematically and the test statistic based on the ratio does not have a closed form expression which makes it impractical for real application. We drive an approximate log-likelihood ratio and propose a multivariate statistical process control chart based on a sequential χ² test to detect a change in the noncentrality parameter. The statistical properties of the proposed test statistic are explored. The average runs length (ARL) performance of the proposed charts is compared with other MCUSUM charts for process mean monitoring. The experimental results reveal that the proposed charts achieve superior, both zero-state and steady-state, ARL performance over a wide range of mean shifts, especially when the dimension of measurements is large.     

Using an experimental design to identify and quantify the effects of environment related test parameters on the in vitro mucoadhesivity testing of a propanolol buccal tablet

This study sought to identify and quantify the effects of environmental test parameters on the mucoadhesivity of a propranolol tablet. Their effects on Maximum Detachment Force (MDF) measurements were evaluated using a Box-Behnken design matrix. Prehydration time (PT) had a statistically significant negative main effect while contact force (CF) had no significant effect on in vitro MDF measurements. While contact time (CT) had no significant main or quadratic effects, it had a positive interaction effect with PT. The mathematical model was statistically validated and a PT of 3.5 min and a CT of 5 min was proposed for mucoadhesion testing by the tensile method during formulation optimization.     

高空模拟试验舱的传热和真空分析与计算

分析了高空模拟试验舱的传热与舱压分布,并提出了计算方法,为高模试验舱的结构设计提供了参考。