A stochastic model for burn‐in procedures in accelerated environment

Burn‐in procedure is a manufacturing technique that is intended to eliminate early failures of system or product. Burning‐in a component or system means to subject it to a period of use prior to being used in field. Generally, burn‐in is considered expensive and so the length of burn‐in is typically limited. Thus, burn‐in is most often accomplished in an accelerated environment in order to shorten the burn‐in process. A new failure rate model for an accelerated burn‐in procedure, which incorporates the accelerated ageing process induced by the accelerated environmental stress, is proposed. Under a more general assumption on the shape of failure rate function of products, which includes the traditional bathtub‐shaped failure rate function as a special case, upper bounds for optimal burn‐in time will be derived. A numerical example will also be given for illustration. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2006     

基于退化速率跟踪粒子滤波的剩余使用寿命预测框架

毋庸置疑,剩余使用寿命预测对于设备的健康管理越来越重要。近年来粒子滤波方法被越来越多地应用到设备寿命预测技术当中,这是因为粒子滤波方法能更好的解决非线性非高斯系统滤波问题,而且能够获得不确定度信息。但该方法的预测性能却过度依赖于预测模型,并且对于模型参数的初始分布也比较敏感,这在一定程度上限制了粒子滤波预测方法的进一步发展。本文针对基本粒子滤波预测方法的不足,提出了一种基于退化速率跟踪粒子滤波的通用预测框架,以历史观测数据的退化速率统计规律作为指导来跟踪目标数据的退化速率,实现对粒子滤波预测方法的简化。并将该方法用于轴承和锂离子电池的剩余使用寿命预测,验证了方法的有效性。     

基于自适应阈值的FAST特征点提取算法

FAST特征提取算法阈值选取固定,因此不能满足不同图像的特征点抽取要求,并且提取的结果存在着多个特征点块的现象。针对这些缺陷,首先采用动态全局阈值对原始灰度图像进行初步提取得到候选特征点,然后采取动态局部阈值和非极大值抑制法进一步对候选特征点进行筛选,从而达到自适应选取阈值和抑制多个特征点块的目的。实验表明,改进后的算法稳定性高,对不同光照和对比度情况下有一定的适应能力,并且运算量相对比于其他一些特征提取算法要小得多,满足实时应用的要求。     

失去润滑条件下弧齿锥齿轮传动系统瞬态温度场Simulink仿真分析

根据传热学理论和热网络法,以某型直升机尾减速器弧齿锥齿轮传动系统为研究对象,建立了其温度场Simulink仿真计算模型。基于该模型,计算获得该传动系统正常润滑条件下的稳态温度场,并以它作为初始条件计算分析该传动系统失去润滑条件下的瞬态温度场,为预测该弧齿锥齿轮传动系统在失去润滑条件下的干运转生存能力提供理论依据。     

Thermal hazard assessment of TKX-50-based melt-cast explosive

In the present study, thermal hazards of TNT and DNAN used as the molten binder in TKX-50-based melt-cast explosives were comparatively studied through accelerating rate calorimeter (ARC) and Cook-off experiments. Two kinds of ARC operation modes were performed to investigate the thermal safety performance under adiabatic conditions (HWS mode) and constant heating (CHR mode). The obtained results demonstrated that at both heating modes, DNAN/TKX-50 outperformed TNT/TKX-50 from the thermal safety point of view. However, the sensitivity to heat of the samples was reverse because of the different heating modes. In addition, the results of thermal hazard assessment obtained from the cook-off experiment complied with ARC analysis which indicated the molten binder TNT replaced by DNAN would reduce the hazard of the TKX-50 melt cast explosive. Furthermore, the results of cook-off experiments also showed that DNAN/TKX-50 outperformed TNT/TKX-50 from the aspect of thermal stability, which was consistent with the result of CHR mode because of the similar heating process.     

Formation of adiabatic shearing band for high-strength Ti-5553 alloy: A dramatic thermoplastic microstructural evolution

By using split Hopkinson pressure bar, optical microscopy and electronic microscopy, we investigate the influence of initial microstructures on the adiabatic shear behavior of high-strength Ti–5Al–5V–5Mo–3Cr (Ti-5553) alloy with lamellar microstructure and bimodal microstructure. Lamellar alloy tends to form adiabatic shearing band (ASB) at low compression strain, while bimodal alloy is considerably ASB-resistant. Comparing with the initial microstructure of Ti-5553 alloy, we find that the microstructure of the ASB changes dramatically. Adiabatic shear of lamellar Ti-5553 alloy not only results in the formation of recrystallized β nano-grains within the ASB, but also leads to the chemical redistribution of the alloying elements such as Al, V, Cr and Mo. As a result, the alloying elements distribute evenly in the ASB. In contrast, the dramatic adiabatic shear of bimodal alloy might give rise to the complete lamination of the globular primary α grain and the equiaxial prior β grain, which is accompanied by the dynamic recrystallization of α lamellae and β lamellae. As a result, ASB of bimodal alloy is composed of α/β nano-multilayers. Chemical redistribution does not occur in ASB of bimodal alloy. Bimodal Ti-5553 alloy should be a promising candidate for high performance armors with high mass efficiency due to the processes high dynamic flow stress and excellent ASB-resistance.     

数字电位器ADN2850及其在光传输校准系统中应用

数字电位器是一种可在计算机控制下,通过编程来实现自动操作的智能化器 件,具有调节精确、稳定,数字可长期保存和随时刷新,体积小、抗振动、寿命长的特点 ADN2850是ANALOG公司生产的一种典型的数字电位器,可以通过SPI接口控制它的工作 模式和阻值。介绍了它的结构和控制命令,着重强调了它的SPI接口技术和在光传输校准 系统中应用,通过C语言控制程序控制其阻值,达到了预期的效果。     

切向空气气流对激光辐照碳纤维复合材料的影响

实验研究了靶材表面存在和不存在切向空气气流时,975nm连续激光对碳纤维增强树脂基复合材料的辐照效应,发现切向气流的加载有利于激光对碳纤维复合材料的破坏.从理论上对激光辐照下碳纤维复合材料的破坏机理进行了初步分析,基于碳的氧化特性和氧化反应机理,推导了碳纤维的氧化速率方程.采用改进的光滑粒子方法,对激光辐照下复合材料树...     

如何估计软件的MTBF

软件剩余初始故障个数No、平均无故障时间MTBF、故障暴露率λ和软件运行的成功率θ等是衡量软件可靠性的重要参数.其中对高可靠性软件(包括军用软件等)MTBF是最重要的.传统的MTBF计算方法有2种一是计算发生故障的平均时间间隔二是通过软件可靠性模型进行估计.前者代价较大,后者不太准确.本文从软件的失败率入手研究软件的MTBF,这是一个比较贴近实际的方法.     

后方油库整体生存概率分析计算

针对我军后方油库特点,探讨了油库整体生存概率计算的基本思路和方法,分析了各类分项目标生存概率的计算方法,采用层次分析对后方油库各分项目标权值进行了详细分析计算,可为后方油库伪装防护效能评估提供依据。