空间斯特林制冷机的可靠性筛选

介绍了中国国内空间斯特林制冷机的早期失效模式及其对应的筛选试验方法,研究了长寿命制冷机的寿命筛选方法,采用温度循环为模拟应力,试验内容包括两部分:制冷机的开关机试验和连续工作试验,总试验时间约500 h.按照给定的筛选程序,可在短期内发现制冷机内部潜在的薄弱环节,诱发其早期失效,剔除不良产品,经过筛选之后的制冷机可有一个长期稳定的工作期,从而提高了制冷机的使用可靠性,推动了自研制冷机在空间任务中的应用.     

整体式斯特林制冷机工程化模型研究

针对国内斯特林制冷机可靠性处于浴盆曲线前端的现状,提出当前斯特林制冷机工程化解决加工、装配误差等引起早期失效的问题.为了指导微型斯特林制冷机工程化研究,对斯特林制冷机的模型进行了比较,得出采用系统动力学方法建立的制冷机模型适合进行工程化研究.在系统动力学观点指导下建立了整体式斯特林制冷机模型,并对该模型的各个环节进行了动力学元件量化的工作,以最新研究成果为例,给出了量化的方法.     

牛津型斯特林制冷机的加速寿命试验

分析了牛津型长寿命斯特林制冷机的主要失效模式、失效机理以及应用特点,提出高温运行的加速寿命评价方法.4 300 h的加速寿命试验结果表明,制冷机性能已明显退化,并呈现污染导致的失效特征,初步验证高温加速污染失效的有效性.     

微型斯特林制冷机可靠性现状及趋势

制冷机的可靠性一直是军用微型斯特林制冷机最重要的性能指标。首先阐述了可靠性的一些基本知识,之后介绍了RICOR、Thales Cryogenics和BAE等几家公司的斯特林制冷机可靠性预测方法。同时还详细介绍了从上个世纪50年代至今国内外军用微型制冷机可靠性水平的增长情况及其发展趋势,最后介绍了一些制冷机常用的可靠性加速方法。     

小型斯特林制冷机动力学设计及试验

介绍了小型斯特林制冷机动力学设计及试验情况。通过试验,验证了斯特林制冷机动力学设计的准确性,达到了制冷机的谐振,降低了功耗,工作稳定性和可靠性得到相应的提高。     

空间斯特林制冷机失效分析

针对空间用的"牛津型"斯特林制冷机的结构特点,对其早期失效模式和正常失效模式等主要失效模式进行了较深入分析,提出了改进措施.通过结构设计、工艺等改进,可以消除早期失效模式、延长正常失效的时间.     

空间用斯特林制冷机的寿命评价

介绍了空间用斯特林制冷机的主要失效模式和失效机理,国内外寿命评价研究的状况和进展,分析了几种加速寿命评价方法.针对中国空间用制冷机寿命评价研究的现状,提出了加速寿命评价的一些见解和思路.     

斯特林制冷机污染失效研究进展

斯特林制冷机内部放气造成的失效严重影响制冷机寿命。制冷机内部放气气体会在回热器冷端及膨胀腔低温表面凝结,降低回热器的回热效率和冷头换热面传热能力,并加大制冷工质流动阻力。主要介绍了斯特林制冷机加速寿命试验和污染放气模拟数值计算方法等,提出了制冷机污染失效研究发展方向。对今后主要研究方向进行了展望。     

星载斯特林制冷技术研究进展

介绍了国外星载长寿命斯特林制冷技术的研究进展及其在空间遥感系统和科学探测卫星中应用情况,并对影响斯特林制冷机工程应用的工作寿命和可靠性进行了简要分析.综述了国内星载斯特林制冷技术的发展现状,最后提出在我国开展星载斯特林制冷机研制的几点建议.     

斯特林制冷机真空环境热模拟试验研究

为了验证空间斯特林制冷与辐射制冷、实现复合制冷系统的可行性,获取斯特林制冷机在真空条件下的散热情况,进行了斯特林制冷机空间真空环境热模拟试验。试验结果表明,真空条件下斯特林制冷机的散热是影响制冷机性能的重要因素。     

Reliability formulation for composite laminates subjected to first-ply failure

Methods formulated on the basis of the concept of first-ply failure and the structural reliability theory are presented for the reliability analysis of laminated composite plates. In the reliability formulation, an appropriate phenomenological failure criterion is used to establish the limit state equation of the laminated composite plates, and different numerical techniques are employed to evaluate the reliability of the plates. Experimental investigations of lamina strengths and first-ply failure loads of laminated composite plates were performed. Baseline probability distributions of lamina strength parameters constructed from the test data are used to study the reliability of the laminated plates. The accuracy of the proposed models in reliability assessment of the laminated plates are verified by the experimental results on first-ply failure load distributions.     

Study on reliability modelling of a hydraulic excavator system

The failure patterns of a well-known brand of a hydraulic excavator system used in different environments were modelled adequately with an NHPP (non-homogeneous Poisson process) having time-dependent log-linear peril rate functions. Using the fitted model, the reliability of the excavator system was estimated in different environments (cement plant, coal mine, iron ore mine, etc.). The system reliability was found to be very poor during the initial phase of operation and gradually improved with an increase in cumulative operating hours regardless of change in environment. Notwithstanding this general trend, the system reliability differed significantly in different environments for any given duration of operation and was particularly very poor in cement plants. With the help of the FMEA technique, high risk prone failure modes of the excavator system of the given model were identified and appropriate corrective measures were initiated. The failure patterns of the modified excavator system changed regardless of environment, so much so that an HPP (homogeneous Poisson process) model with constant peril rate could be fitted adequately to characterize the failure pattern of the system. The system reliability improved considerably in the initial phase of operation since start-up.     

相依失效生命线工程系统抗震可靠度估计的统一RDA算法

在网络连通可靠度分析的递推分解算法(Recursive Decomposition Algorithm,简称RDA)的基础上,先整合原RDA算法中分别用于不同网络赋权形式的三部分程序,发展出统一RDA算法。应用顺序复合法(Sequential Compounding Method,简称SCM)和Gumbel Copula函数分别计算RDA算法中不交最小路和不交最小割事件的联合失效概率,解决元件相依失效生命线工程系统的抗震可靠度估计问题,最终发展出相依失效生命线工程系统抗震可靠度估计的统一RDA算法。36节点格栅型网络可靠度案例计算结果表明:此方法可以用于相依失效网络系统的动力抗震可靠度估计,计算精度较高。     

Modelling and Simulation of Scraper Reliability for Maintenance

A scraper conveyor is a kind of heavy machinery which can continuously transport goods and widely used in mines,ports and store enterprises.Since scraper failure rate directly affects production costs and production capacity,the evaluation and the prediction of scraper conveyor reliability are important for these enterprises.In this paper,the reliabilities of different parts are classified and discussed according to their structural characteristics and different failure factors.Based on the component’s time-to-failure density function,the reliability model of scraper chain is constructed to track the age distribution of part population and the reliability change of the scraper chain.Based on the stress-strength interference model,considering the decrease of strength due to fatigue failure,the dynamic reliability model of such component as gear,axis is developed to observe the change of the part reliability with the service time of scraper.Finally,system reliability model of the scraper is established for the maintenance to simulate and calculate the scraper reliability.     

基于Copula函数的并联结构系统可靠度分析

不完备概率信息条件下变量联合分布函数的确定及其对结构系统可靠度的影响还缺少系统地研究,该文目的在于研究表征变量间相关性的Copula函数对结构系统可靠度的影响规律。首先,简要介绍了变量联合分布函数构造的Copula函数方法。其次,提出了并联系统失效概率计算方法,并推导了相应的计算公式。最后以几种典型Copula函数为例研究了Copula函数类型对结构并联系统可靠度的影响规律。结果表明:表征变量间相关性的Copula函数类型对结构系统可靠度具有明显的影响,不同Copula函数计算的系统失效概率存在明显的差别,这种差别随构件失效概率的减小而增大。当并联系统的失效区域位于Copula函数尾部时,Copula函数的尾部相关性对系统可靠度有明显的影响,计算的失效概率比没有尾部相关性的Copula函数的失效概率大。当组成并联系统的两构件功能函数间正相关时,系统失效概率随相关系数的增大而增加;当构件功能函数间负相关时,系统失效概率随相关系数的增大而减小。此外,无论构件失效概率和变量间相关系数如何变化,Copula函数计算的失效概率都位于系统失效概率的上下限内。     

联合分布函数构造的Copula函数方法及结构可靠度分析

不完备概率信息条件下变量联合分布函数的确定及其对结构可靠度的影响还缺少系统地研究。为此,提出了基于Copula函数的变量联合概率分布函数构造方法,并分析了不同Copula函数类型对结构可靠度的影响规律。首先,简要介绍了基于Copula函数的变量联合分布函数构造方法。其次,提出了构件失效概率计算的直接积分方法。最后以构件可靠度问题为例研究了Copula函数的类型对结构可靠度的影响规律。结果表明:不完备概率信息条件下构件可靠度是不唯一的,表征变量间相关性的Copula函数类型对构件可靠度具有明显的影响,不同Copula函数计算的构件失效概率存在明显的差别,这种差别随构件可靠指标的增大(或失效概率的减小)而增大。Copula函数尾部相关性对结构可靠度具有重要的影响。当功能函数的失效区域位于Copula函数尾部时,计算的失效概率明显比没有尾部相关性的Copula函数的失效概率大。基于功能函数的均值和标准差计算的可靠指标不能反映Copula函数的类型对结构可靠度的影响,而基于功能函数实际分布求得的失效概率则可以有效反映不同Copula函数对结构可靠度的影响。     

Reliability predictions of laminated composite plates with random system parameters

Reliability predictions of laminated composite plates with random system parameters subjected to transverse loads are performed using different methods. System parameters such as material properties, layer thicknesses, and lamina strengths of a laminated composite plate are treated as base-line random variables and an appropriate failure criterion is used to construct the limit state equation of the plate in the reliability analysis. Based on the statistics of the base-line random variables obtained from experiments, different methods, namely, Monte Carlo method, β method, and first-order second moment method, are used to calculate the reliability of the laminated composite plates. In the first-order second moment method, the stochastic finite element method is used to derive for the statistics of the first-ply failure load of the laminated composite plates from those of the base-line random variables. The reliability of the laminated plate is then computed using the theoretically determined statistics together with an assumed probability distribution function of the first-ply failure load. The feasibility and accuracy of the different methods are studied by means of the experimental data of centrally loaded laminated composite plates with different lay-ups. The suitability of several commonly used failure criteria for reliability analysis of laminated composite plates is also investigated by means of several examples.     

Non-invariant failure probabilities with invariant reliability index

This paper presents a critical examination of some basic limit state functions that led to development of the invariant code format for reliability analysis. Proper methods of evaluating failure probabilities from these limit state functions are used to check failure probabilities estimated by reliability index methods, and the results show that failure probability for a limit state function that may assume different but seemingly equivalent forms is not always invariant as the invariant format would indicate.     

Reliability analysis against progressive failure of TLP tethers in extreme tension

The tension leg platform (TLP) is a moored floating structure whose buoyancy is more than its weight. The mooring system of TLP consists of number of tensioned tethers connected to the columns at the top and anchored to the seabed at the bottom. These tethers are vulnerable to failure due to extreme (maximum and minimum) tensions. The reliability study of these tethers is an important subject of study. The reliability may further deteriorate after the failure or removal of any of these tethers. In the present study, reliability analysis of an intact TLP and TLP with one tether missing has been carried out. A Von-Mises failure criterion has been adopted to define the failure of tether against maximum tension. The minimum tension failure occurs when the tethers slack due to loss of tension. The limit state functions for maximum and minimum tension cases have been derived. The computationally efficient algorithm First order reliability method (FORM) has been adopted for reliability calculations. Results are presented in terms of reliability indices and probabilities of failure for each sea state. The probabilities of failure so obtained for different sea states have been used for the assessment of annual and life time probability of failures. Reliability of the TLP with one tether missing has been compared with that of the corresponding intact TLP. Effect of wind has also been studied on the progressive failure of TLP tethers and the results have been compared with that of an intact TLP.     

Field Failure Data: an Alternative Proposal for Reliability Estimation

Product reliability is a very important issue for the competitive strategy of industries. In order to estimate a product's reliability, parametric inferential methods are required to evaluate survival test data, which happens to be a fairly expensive data source. Such costly information usually imposes additional compromises in the product development and new challenges to be overcome throughout the product's life cycle. However, manufacturers also keep field failure data for warranty and maintenance purposes, which can be a low‐cost data source for reliability estimation. Field‐failure data are very difficult to evaluate using parametric inferential methods due to their small and highly censored samples, quite often representing mixed modes of failure. In this paper a method for reliability estimation using field failure data is proposed. The proposal is based on the use of non‐parametric inferential methods, associated with resampling techniques to derive confidence intervals for the reliability estimates. Test results show the adequacy of the proposed method to calculate reliability estimates and their confidence interval for different populations, including cases with highly right‐censored failure data. The method is shown to be particularly useful when the sampling distribution is not known, which happens to be the case in a large number of practical reliability evaluations. Copyright © 2006 John Wiley & Sons, Ltd.