20cm氙离子推力器加速栅寿命预测

电荷交换离子对加速栅的腐蚀引起的加速栅结构失效是影响离子推力器寿命的主要因素之一。利用离子推力器加速栅工作寿命的确定性预测模型对兰州物理研究所研制的20cm氙离子推力器加速栅极结构失效时的质量损失和地面运行寿命进行了计算,将计算结果与地面寿命实验结果进行了对比,并利用该模型对20cm氙离子推力器加速栅极空间运行寿命进行了预测。     

LIPS-200离子推力器电子反流极限不确定度分析

针对延长离子推力器栅极极限寿命的恒定加速电压和步进调节加速电压两种优化方法的工程应用需求,结合现有LIPS-200离子推力器产品技术参数,基于电子反流极限的Williams解析表达并应用QMU工程方法,定量计算了LIPS-200离子推力器电子反流极限的不确定度.计算结果表明:不确定度主要影响因素包括束流电子温度、加速栅...     

不同本底压力下离子推力器电子反流失效的数值模拟

针对20cm氙离子推力器具体设计和工作参数,采用二维轴对称模型的网格质点和蒙特卡罗碰撞方法模拟计算了氙离子和氙原子在离子推力器栅极系统中的运动.模拟得到了在不同本底压力下交换电荷离子对加速栅极孔壁的溅射腐蚀情况,并由此计算了不同本底压力下因孔壁腐蚀导致发生电子反流失效模式的推力器工作寿命.     

离子推力器栅极系统仿真典型验证技术研究现状

栅极系统是影响离子推力器性能和寿命的重要组件之一,数值仿真建模方法是研究栅极系统失效机理的重要手段。为了提高数值仿真模型运算结果的置信度,需要对栅极系统仿真模型开展试验验证研究。本文在对栅极系统工作物理过程、失效模式和失效机理分析的基础上,系统调研了国内外离子推力器栅极系统仿真的研究进展,并重点对栅极系统仿真模型验证技术研究进展开展了调研,为离子推力器栅极系统仿真模型验证研究提供了参考。     

双阳极磁增强真空弧推力器性能试验研究

为了提高真空弧推力器的工作寿命,研制了一款能够提供三种放电模式的双阳极磁增强真空弧推力器(Bi-Anode MVAT).开展了引弧试验、不同放电模式下推力性能比较试验、失效模式验证试验和寿命考核试验研究.试验结果表明,双阳极放电模式下外界注入脉冲能量对推力器元冲量的平均转化率为1.7μN·s/J,10 Hz下连续放电超...     

栅极系统电子返流对离子推力器寿命影响

栅极系统电子返流是离子推力器寿命的主要失效模式之一。以20 cm Xe离子推力器地面运行测试数据为基础,结合离子推力器栅极系统电子返流失效机理,预测了离子推力器在地面测试环境中和空间飞行环境中栅极系统电子返流对寿命的影响。预测结果表明:20 cm Xe离子推力器在地面试验环境中和空间飞行环境中的预期寿命分别为6 600 h和17 000 h。     

基于确信可靠度的离子推力器可靠性分析和试验设计

针对小行星探测用LIPS-300离子推力器多工况、长寿命、高可靠和极端小子样特征,提出了一种基于确信可靠度理论的可靠性评估方法,适用于当前离子推力器服役过程中性能退化不确定性情况下的可靠性评估。首先对离子推力器进行了功能、性能和裕量分析（Function,Performance and Margin Analysis,FPMA）,识别和确定了离子推力器的关键失效模式为电子反流,并确定了电子反流这一失效模式对应的性能参数及阈值;其次在FPMA基础上完成了离子推力器裕量方程、退化方程和可靠性度量方程的建立;最后,为了验证可靠性评估模型的准确性,在综合考虑地面试验技术条件和背景任务的基础上设计了针对关键失效模式电子反流的试验方案。     

离子推力器加速栅寿命的概率性分布和可靠性预测

利用蒙特卡罗（Monte Carlo）方法对离子推力器加速栅寿命进行了模拟。得出了20 cmXe离子推力器加速栅寿命的概率性分布和不同寿命预期下的可靠性,发现加速栅寿命分布近似服从高斯分布。在推力器工作压力小于时,对加速栅不同寿命预期下的可靠度进行了预测,发现运行寿命达到3 000 h的可靠度为0.90。     

本底真空对推力器加速栅截获CEX离子电流

离子推力器地面寿命考核和加速寿命试验是在地面真空舱中进行的,真空舱本底真空会对离子推力器性能和寿命特别是加速栅截获电流有重要影响.为了确定20 cm氙离子推力器地面试验本底压力,本文采用PIC-MCC方法,计算了不同本底真空下栅极系统中性原子位置、密度分布和交换电荷(Charge Exchange,CEX)离子位置、速度和密度分布.模拟计算了在不同真空舱本底真空下20 cm氙离子推力器加速栅极截获的CEX离子电流,与实验结果符合较好,并通过理论方法确定了加速栅电流随真空舱本底真空变化的“拐点”.计算结果可以为离子推力器长寿命考核试验和栅极系统加速寿命试验真空舱本底真空的选择提供了参考.     

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.     

用加速寿命试验法研究瓦楞纸箱寿命初探

选用空气相对湿度H和垂直载荷G为加速应力，用加速寿命试验法对瓦楞纸箱寿命进行研究，建立了瓦楞纸箱双应力加速方程，并计算出正常工作应力下瓦楞纸箱的平均寿命及可靠度。     

Bayesian and regression approaches to on-line prediction of residual tool life

In this paper, two statistical approaches to on-line prediction of cutting tool life are presented and discussed. A Bayesian approach utilizes in-process information about the cutting tool state and constitutes a valuable basis for improved prediction. A second approach is based on the cutting forces and facilitates a prediction of the tool life with an uncertainty of 15% after 1.5–2.0 cutting minutes. Traditional tool condition monitoring can be improved by increased reliability of tool life predictions, increased utilization of the cutting tools together with reduced need for pre-process data and calibrating procedures. © 1998 John Wiley & Sons, Ltd.     

产品生命周期成本概念及分析方法

随着人们成本意识的增强,生命周期成本日益引起设计者和用户的重视。对产品生命周期和产品生命周期成本概念进行了论述,介绍了参数模型、类推模型和详细模型3种生命周期成本分析模型,最后以某厂计划购买自动包装生产线为例,说明如何利用生命周期成本概念进行投资决策分析。     

基于生活方式的包装设计新探

以包装设计在现实生活中的传播交流为启示,分析了包装与生活方式的关系,从生活包装和商品包装两方面阐述了不同时期包装所呈现的不同形式,进而分析了包装作为设计的一部分,丰富了人们的生活,同时包装的内涵也发生了深刻的变化。在此基础上,提出了包装设计的目的是为了人,具体说是为人创造合理的生活方式,随着包装的改变人们的生活方式也日益发生变化。     

基于老年生活需求的APP应用设计

目的 研究现代老年生活中的信息需求、身体变化和生活重心的转移对APP设计的影响。方法 根据马斯洛需求层次理论得到老年人的信息需求包括各个层面，比如生理信息需求、安全信息需求、情感信息需求、受尊重的信息需求与自我实现的信息需求。根据老年人的身体现状变化，阐释老年人在视觉、听觉、触觉和行为能力上对APP设计的特别要求。在生活重心转移和现代生活方式发生巨变的现实中，分析老年人对APP应用的选择趋势。结论 满足老年人生活需求的APP规划设计，需要充分考虑老年人的信息需求、生理变化和现实生活状况等，力求操作简洁，功能设置单一化，界面设计清晰化，流程安排直线化。在APP内容设置中既要照顾老年人多层次的信息需求，也要从生活便利、健康保障、益智娱乐等多方面提供专项APP设计开发，吸引老年人积极地融入现代生活的新模式中来。     

Variation mode and effect analysis: an application to fatigue life prediction

We present an application of the probabilistic branch of variation mode and effect analysis (VMEA) implemented as a first‐order, second‐moment reliability method. First order means that the failure function is approximated to be linear around the nominal values with respect to the main influencing variables, while second moment means that only means and variances are taken into account in the statistical procedure. We study the fatigue life of a jet engine component and aim at a safety margin that takes all sources of prediction uncertainties into account. Scatter is defined as random variation due to natural causes, such as non‐homogeneous material, geometry variation within tolerances, load variation in usage, and other uncontrolled variations. Other uncertainties are unknown systematic errors, such as model errors in the numerical calculation of fatigue life, statistical errors in estimates of parameters, and unknown usage profile. By treating also systematic errors as random variables, the whole safety margin problem is put into a common framework of second‐order statistics. The final estimated prediction variance of the logarithmic life is obtained by summing the variance contributions of all sources of scatter and other uncertainties, and it represents the total uncertainty in the life prediction. Motivated by the central limit theorem, this logarithmic life random variable may be regarded as normally distributed, which gives possibilities to calculate relevant safety margins. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of hardness on multiaxial fatigue behaviour and some simple approximations for steels

Constant-amplitude in-phase and 90° out-of-phase axial-torsional fatigue tests were conducted on tubular specimens made from a medium-carbon steel with three hardness levels obtained from normalizing, quenching and tempering and induction hardening to find the effect of hardness on multiaxial fatigue behaviour. In addition, the same loadings were applied on the normalized solid specimens to investigate the effect of specimen geometry on multiaxial fatigue life. Similar fatigue life variation as a function of hardness was found for in-phase and out-of-phase loadings, with higher ductility beneficial in low-cycle fatigue (LCF) and higher strength beneficial in high-cycle fatigue (HCF). Multiaxial fatigue data were satisfactorily correlated for all hardness levels with the Fatemi–Socie parameter. Furthermore, in order to predict multiaxial fatigue life of steels in the absence of any fatigue data, the Roessle–Fatemi hardness method was used. Multiaxial fatigue lives were predicted fairly accurately using the Fatemi–Socie multiaxial model based on only the hardness level of the material. The applicability of the prediction method based on hardness was also examined for Inconel 718 and a stainless steel under a wide range of loading conditions. The great majority of the observed fatigue lives were found to be in good agreement with predicted lives.     

A plausible strategy for modeling fatigue life variation

In this paper stochastic modeling is used to predict fatigue life uncertainty by simulating small variations in strain-life material constants. The Monte Carlo method,^[1] using either known cumulative distribution functions (CDFs) for the material constants and/or postulated CDFs, provides the mechanism to generate a set of failure data. These data are analyzed, using ordinary statistical techniques, to develop the Weibull CDF for cycles to failure. It is seen that small variations (∼±15%) in values of the strain-life constants result in large variations (∼600%) in predicted fatigue life at moderate strain. The often-observed phenomenon that spread in fatigue data is greater at lower strain is also described by the stochastic model.     

QStE380TM SEW092钢疲劳性能研究

对QStE380TM SEW092材料进行疲劳试验,得到了应力-寿命曲线,当σ＞σ0.1时,N＝6.722×1041×σ-13.196,σ0.1＝335MPa;得到了应变疲劳特性△σ/2＝919(2Nf)-0.0923,△εp/2＝L 08(2Nf)-0.7599,△σ/2＝912(△εpp/2)0.1204.其裂纹扩展速率为当da/dN≥5×10-5mm/周,da/dN＝L 041×10-9(△K)3.3012;当da/dN＜5×10-5mm/周,da/dN＝3.747×10-12(△K)6.8595.     

The Constant Shape Parameter Assumption in Weibull Regression

ABSTRACT

The usual assumption in Weibull regression is that the scale parameter is a function of the predictor variables, and the shape parameter is constant. We consider the problem of estimating parameters in the presence of a nonconstant shape parameter and the effect of assuming a constant shape parameter when it really is not constant. We consider both classical and Bayesian methods of estimation. The misspecification of a constant shape parameter can lead to a loss of power for tests regarding the slope parameters. We find that prediction intervals can be inaccurate when the shape parameter is incorrectly assumed to be constant.