Quasi-static tensile behavior of large-diameter thin-walled Ti–6Al–4V tubes at elevated temperature

As promising light-weight and high-performance structure components, large-diameter thin-walled(LDTW) Ti–6Al–4V titanium alloy(TC4) bent tubes are needed most urgently in many industries such as aviation and aerospace. Warm bending may be a feasible way for manufacturing these components. Understanding their temperature and strain rate dependent tensile behavior is the foundation for formability improvement and warm bending design. In this paper, uniaxial tensile tests were conducted at elevated temperatures ranging from 298 K to 873 K at tensile velocities of 2, 10, 15 mm/min. The main results show that the tensile behavior of LDTW TC4 tubes is different from that of TC4 sheets. The typical elongation of TC4 tubes at room temperature is 10%lower than that of TC4 sheets. The flow stress of TC4 tubes decreases greatly by about 50% with the temperature rising to 873 K. At temperatures of 573–673 K, the hardening exponent is at its highest value, which means the deformation mechanism changes from twining to more dislocation movement by slipping. The fracture elongation of TC4 tubes fluctuates with increasing temperature,which is associated with changes in the deformation mechanism and with the blue brittleness. The fractography of TC4 tubes at various temperatures, especially at 673 K, shows that second phases and impurities significantly influence fracture elongation. By considering the characteristics of the tensile behavior and by properly choosing the die material, the warm bending for TC4 tubes can be achieved at temperatures of 723–823 K.     

布拉格光栅植入角度对在复合材料中传感检测特性影响

植入到复合材料内部的布拉格光栅可用于监测复合材料内部应力应变及温度变化,但是现有研究里对于光栅植入过程中对光栅传感检测特性造成的影响却未见报道。在植入过程中,植入光栅与碳纤维存在的夹角将会产生内应力,这会对光栅传感检测效果产生影响。为了研究其影响规律,通过将光栅植入到准各向同性复合材料的不同层中,研究光纤与相邻预浸带中碳纤维之间的夹角对温度与应力检测特性影响。研究结果表明:光栅植入角度会对其温度和应变传感检测特性造成较大影响,当光栅与相邻预浸带碳纤维存在夹角时,光栅拉伸应变测量值与应变片测量值出现偏差,发生啁啾现象;同时光栅与相邻预浸带碳纤维的夹角越大,光栅温度检测曲线线性拟合度越差。     

大型挠性结构航天器姿态精确指向控制

针对空间大型挠性结构航天器姿态精确指向控制中，执行机构振动和挠性结构变形对载荷指向带来的高频和低频扰动，提出了多环路复合控制策略，在传统姿态控制闭环回路的基础上，引入执行机构隔振回路和载荷指向精确控制回路，实现对执行机构振动的隔离和对载荷指向的精确补偿，并设计了回路的闭环控制方法。数学仿真和部分试验结果表明，该方法能够有效提升载荷指向精度。     

新型针式高压隔离阀的设计和试验

空间推进任务有时需要气体推进剂在高压贮箱内密闭长达数年,隔离阀作为隔离贮箱内高压气体推进剂的装置,不仅要求在数年后可正常启动,而且在高压条件下必须严格控制推进剂的泄漏量。因此,提出了一种新型高压气体隔离阀,其采用中空启动针穿破隔离装置的启动方式以减小金属碎屑对气体微通道的影响。对该隔离阀进行了开启验证试验,并以开启隔离阀前后通过启动针的气体流量之比作为一个重要参数,分析了金属碎屑对气体微通道的影响。结果表明:开启隔离阀的功率约为5.6 W,满足微小卫星对低功率的严格要求;同时气体流量之比约为95%,可认为金属碎屑对气体微通道的影响比较小。     

GA-Based Model Predictive Control of Semi-Active Landing Gear

Semi-active landing gear can provide good performance of both landing impact and taxi situation, and has the ability for adapting to various ground conditions and operational conditions. A kind of Nonlinear Model Predictive Control algorithm （NMPC） for semi-active landing gears is developed in this paper. The NMPC algorithm uses Genetic Algorithm （GA） as the optimization technique and chooses damping performance of landing gear at touch down to be the optimization object. The valve＇s rate and magnitude limitations are also considered in the controller＇s design. A simulation model is built for the semi-active landing gear＇s damping process at touchdown. Drop tests are carried out on an experimental passive landing gear systerm to validate the parameters of the simulation model. The result of numerical simulation shows that the isolation of impact load at touchdown can be significantly improved compared to other control algorithms. The strongly nonlinear dynamics of semi-active landing gear coupled with control valve＇s rate and magnitude limitations are handled well with the proposed controller.     

对特定传感器故障敏感的最优奇偶向量检测与隔离方法

 提出了一种利用对特定传感器故障敏感的最优奇偶向量进行故障检测与隔离的方法。主要思想是设计一个性能指标函数，使得最优奇偶向量对被检测的传感器故障最敏感，而对其余传感器故障和未知输入不敏感。与常用的广义似然比方法相比，该方法明显地提高了故障的检测能力，此外，对故障的隔离效果也更好。     

飞机导航数据仿真系统设计

某型航空相机系统为了清晰地获取目标图像,需要机载导航设备实时提供飞机的姿态和运动信息。某型相机飞机导航数据仿真系统提供了相机需要的ARINC429总线及ARINC407总线数据,满足相机研制和调试的要求。试验证明,系统运行稳定,数据接收准确,可靠性高。     

小卫星故障诊断与处理技术

介绍一种简单有效的故障诊断及处理技术，它将小卫星的故障分为分系统级，系统级和系统外部级三种，并由星务管理软件处理系统级故障，在每个循环周期都对遥测参数进行采集和监测，故障发生时，根据故障的优先级，选择并恢复具有最高优先级的故障。该技术在某小卫星中应用，能有效满足系统控制周期的限制和系统可靠性要求。     

复合固体推进剂定应变测试研究

考察了拉伸速率，试件夹持方式，环境温度、湿度等多种因素对推进剂定应变性能和测试数据重视性的影响，提出了推进制定应变测蔗的试验条件。     

小型化三向阻尼隔振器

根据对隔振系统的共振传递频率所作的计算，为箭上电子设备选择了ＺＮＱ型阻尼圈组成的三向阻尼隔振器，试验证明了这种隔振器的隔振效果。