Effects of traverse speed on weld formation,microstructure and mechanical properties of ZK60 Mg alloy joint by bobbin tool friction stir welding

ZK60B (Mg-6% Zn-0.6% Zr) alloy joints fabricated by bobbin tool friction stir welding (BTFSW) with various traverse speeds were investigated. The sound joint fabricated by the BTFSW was possible under the appropriate welding parameters. The severe plastic deformation during BTFSW resulted in dispersion and segregation of the Zr-rich particles within the stirred zone (SZ) followed by evolution of a bimodal grain structure with distributed bands of 0.8–1.7 μm ultrafine grains and 4.1–7.1 μm equiaxed grains. Micro-hardness of SZ is substantially reduced in contrast to that of parent metal (PM) in spite of the finer grain size owing to dissolution of Mg-Zn based precipitates having hardening effects on alpha-Mg matrix. With the decrease in traverse speed, randomization degree of the plasticized metal flow increases, which is evidenced by the randomized arc line pattern at the low traverse speed. Among all defect-free joints, the 200 mm/min joint exhibits the weakest isotropy of texture within SZ and the best tensile properties, which has reduced ultimate tensile strength and yield strength by 5.4% and by 22.2%, respectively, as compared to the PM. The randomized texture hinders the joint fracturing within SZ at low elongation. Therefore, a relatively high elongation of 10.8% was achieved, which corresponded to 72% of the PM value.     

非平行边界层C型失稳的非线性演化(英文)

提出用抛物化稳定性方程(PSE)新方法,研究非平行边界层从层流向湍流转捩的C型失稳的演化过程,特别是非线性演化问题。研究了至关重要的初始条件,包括各扰动谐波的初始解、初始站均流变形的模拟、以及通过对线性 PSE 的求解获得 TS波和C型亚谐扰动的初始站值等。发展了高精度的数值方法,满足PSE的关键性正规化条件,实现非线性抛物化稳定性方程的有效求解和稳定推进。算例展示了Blasius边界层的C型失稳的非线性演化过程,与典型实验结果相吻合。     

TiB2颗粒诱导AlSi5电弧增材微观组织演变及性能研究

铝合金的电弧增材制造过程中因持续热积累而引起组织分布不均匀和溶质偏析,导致其性能各向异性。针对这一问题,设计了TiB₂纳米颗粒添加铝合金的钨极氩弧(Tungsten inert gas,TIG)增材制造工艺。在电弧增材制造过程中,通过表面预涂层的方式将纳米TiB₂颗粒添加到试样中,对比研究了纳米TiB₂颗粒不同质量分数对AlSi5合金微观组织的影响。结果表明,随着TiB₂质量分数的增加,AlSi5合金的微观组织不均匀性得到明显改善,1.5%TiB₂的添加使AlSi5合金的晶粒尺寸从226μm减小到85.6μm,且引起(110)和(112)基面上的织构明显减弱,最大取向密度呈下降的趋势;与无颗粒添加的AlSi5增材试样相比,颗粒添加后的沉积层硬度与弹性模量均得到显著提高,硬度值从879MPa增加到1253MPa,弹性模量从81.9GPa增加到88.3GPa。     

A novel testability model for health management of heading attitude system

Prognostics and health management (PHM) is very important to guarantee the reliability and safety of aerospace systems, and sensing and test are the precondition of PHM. Integrating design for testability into early design stage of system early design stage is deemed as a fundamental way to improve PHM performance, and testability model is the base of testability analysis and design. This paper discusses a hierarchical model-based approach to testability modeling and analysis for heading attitude system health management. Quantified directed graph, of which the nodes represent components and tests and the directed edges represent fault propagation paths, is used to describe fault-test dependency, and quantitative testability information is assigned to nodes and directed edges. The fault dependencies between nodes can be obtained by functional fault analysis methodology that captures the physical architecture and material flows such as energy, heat, data, and so on. By incorporating physics of failure models into component, the dynamic process of a failing or degrading component can be projected onto system behavior, i.e., system symptoms. Then, the analysis of extended failure modes, mechanisms and effects is utilized to construct fault evolution-test dependency. Using this integrated model, the designers and system analysts can assess the test suite’s fault detectability, fault isolability and fault predictability. And heading attitude system application results show that the proposed model can support testability analysis and design for PHM very well.     

圆棒阴极展成电解加工间隙特性的研究

建立了圆棒阴极展成电解加工的数学物理模型并以计算机求解，根据计算结果提出了加工间隙的简便算法。经试验验证，该简便算法在工程上是可行的，最后分析了工艺参数对加工间隙的影响。     

Some implications of high luminosity and fast variability in active galactic nuclei

An analysis of the variability timescale against bolometric luminosity for Active Galactic Nuclei shows that a number of sources violate the Eddington limit. The average ratio (L/L_E) is found to change according to group classification. Whilst Seyfert Galaxies have luminosites well within the Eddington limit, Quasars and BL Lac object tend to approach and exceed this limit. Furthermore, BL Lac objects may be further subdivided on the basis of their (L/L_E) ratio. The data on luminosity and variability timescale indicate the existence of two types of active galaxies, one having highly anisotropic emission, probably collimated into jets with pointing angles within few degrees to the line of sight, and the other relating to isotropic emission of photons from the nuclear region. The results are discussed in the light of the high γ-ray luminosity suggested by recent observations of active galaxies.     

大型低轨星座构型演化分析及维持控制策略研究

针对大型低轨星座构型维持控制问题,搭建了一套星座构型演化及维持控制分析流程,适用于千颗量级的大型低轨Walker卫星星座构型演化分析及维持控制;采用去平均漂移偏差的相对构型保持方法分析星座构型演化情况,有效减小了控制频次、均衡了控制卫星分布;采用自由段维持策略有序规划各卫星位置维持控制时序和控制弧段,实现了整个星座在时间和空间维度有序、分散的控制,降低了对星座服务性能的影响。     

一种喷口控制的多目标约束设计方法

为克服试凑法在控制回路参数优化中的局限性,针对涡扇发动机在加力状态易出现喷口摆动的不协调现象,考虑喷口双环控制结构工作特点,采用按需正向设计策略,按照控制系统时域、频域性能指标设计要求,制定兼顾频域、时域性能要求的内、外环协调控制的设计目标准则,提出一种喷口控制的多目标约束的差分进化内外环控制参数自整定优化设计方法,在双转子涡扇发动机非线性模型上进行闭环控制系统仿真验证。结果表明：在飞行高度从0增加到10 km、飞行马赫数从0加速到0.9的起飞和爬升状态进入加力过程以及平飞中保持飞行马赫数不变的关断加力过程中,发动机未出现喷口摆动等现象,涡轮落压比最大相对误差不大于1.5%,喷口闭环控制系统具有期望的伺服跟踪和抗飞行条件变化干扰能力。     

Characterization and life prediction of single-pass honing tool for fuel injection nozzle

Single-pass honing is an important machining method for finish machining of holes, which can meet the requirement for high efficiency and consistency of holes. Characterization and life prediction of single-pass honing tool are necessary to improve the machining accuracy of holes honed, especially dimension accuracy. Single-pass honing tool is a single layer abrasive tool with fixed dimension, which still remains problematic for characterization and life prediction. For fuel injection nozzles with bore diameter under 1 mm, the stiffness of the single-pass honing tool is poor. This article presents a novel analytical model that predicts life of the tool with poor stiffness. Firstly, according to the bore diameter and dimension tolerance, the single-pass honing tool is designed and manufactured. Based on the prepared single-pass honing tool, the measurement and characterization methods are established. Furthermore, the tool wear tests are carried out, and the tool contour evolution model is established to predict the tool life.     

对接机构真空热试验外热流模拟方案研究

根据对接机构的结构特点和真空热试验要求,提出了红外笼、电加热片,以及红外笼+加热片组合3种对接机构外热流模拟方案.仿真计算了在真空罐模拟环境中各方案对接机构构件的稳态温度分布,并与轨道环境进行了比较.确定了最大温差构件.结果表明:红外笼方案较简单,适于正样飞行产品;电加热片和红外茏+加热片方案的地面模拟准确性较佳,适于初样地面产品试验.