基于数字图像相关的预腐蚀2024-T4铝合金疲劳开裂实验研究

通过三维数字图像相关(3D-DIC)方法研究预腐蚀2024-T4铝合金在三种不同最大应力水平和应力比下的疲劳开裂行为。通过应变场演化直观地显示裂纹萌生和扩展的时空特征,并通过扫描电镜观测关键损伤区域的断裂微观形貌。结果表明:试样边缘的局部腐蚀促进了疲劳裂纹萌生,影响了裂纹的形核位置,并引起材料氢脆现象;疲劳裂纹扩展方向与加载方向呈60°~68°角,表明疲劳裂纹扩展可以用KⅠ/KⅡ混合模式来描述;预腐蚀铝合金疲劳失效存在单裂纹断裂、多裂纹联合、多裂纹竞争和多裂纹平行扩展4种典型的失效模式。     

Joining of SiO2 ceramic and TC4 alloy by nanoparticles modified brazing filler metal

Nano-Al₂O₃ particles modified AgCuNi filler was adopted to braze the SiO₂ ceramic and TC4. The effects of filler size as well as the brazing temperature on the interfacial microstructure and mechanical property of the joints were investigated. Nanoscale filler reduced the phases dimension and promoted the homogeneous distribution of microstructure, obtaining a higher joint strength when compared to microscale filler. The increase of brazing temperature made the accelerating dissolution and diffusion of Ti, which promoted the increase of thickness of Ti₄O₇ + TiSi₂ layer adjacent to SiO₂ ceramic and diffusion layer zone nearby TC4 alloy. The hypoeutectic structure was produced in the brazing seam due to the high Ti content. The maximum shear strength of ∼40 MPa was obtained at 950 °C for 10 min.     

GOCE star tracker attitude quaternion calibration and combination

We analyse the inter-boresight angles (IBA) measured by the star trackers on board the GOCE satellite and find that they exhibit small offsets of 7–9″ with respect to the ones calculated from the rotation of the star tracker reference frames to the satellite reference frame. Further, we find small variations in the offsets with a peak-to-peak amplitude of up to 8″, which correlate with variations of the star trackers’ temperatures. Motivated by these findings, we present a method for combining the attitude quaternions measured by two or more star trackers that includes an estimation of relative attitude offsets between star trackers as a linear function of temperature. The method was used to correct and combine the star tracker attitude quaternions within the reprocessing of GOCE data performed in 2018. We demonstrate that the IBA calculated from the corrected star tracker attitude quaternions show no significant offsets with respect to the reference frame information. Finally, we show that neglecting the star tracker attitude offsets in the processing would result in perturbations in the gravity gradients that are visible at frequencies below 2?mHz and have a magnitude of up to 90?mE. The presented method avoids such perturbations to a large extent.     

“忠诚僚机”式有人/ 无人机协同作战概念 与任务管理技术研究

“忠诚僚机”式作战概念定义了有人机与无人机协同作战的新理念，颠覆了传统作战模式。在有人/ 无人机协同作战过程中，有人机以指挥者的角色，对作战任务进行分解、分配与管理。实现有人/ 无人机编队 之间在时间、空间上的协同与配合，而无人机在有人机的指挥下完成侦察与打击等任务。     

面向全月球探测的天基中继测控系统设计

中继测控是月球探测任务中必须解决的关键问题，特别是月球背面和两极地区的着陆和巡视探测任务以及载人登月任务。本文首先对国内外月球中继测控卫星的研究和发展情况进行了调研，分析了未来全月球探测对中继测控的需求。在此基础上，重点给出了面向全月球探测任务的天基中继测控系统设计方案，并仿真分析了该方案的中继测控性能。最后给出了简要的卫星设计方案。     

Investigation on surface integrity of electron beam melted Ti-6Al-4 V by precision grinding and electropolishing

Electron beam melting (EBM), as an excellent Additive Manufacturing (AM) technology, enables the printing of Ti-6Al-4 V alloy for a wide range of applications such as aerospace and biomechanical industries. It improves functionality and integrity of components and negates complexities in assembly processes. However, due to the poor surface and sub-surface integrity represented by the rough surface finish and low dimensional accuracy, achieving a favorable surface condition is quite challenging. Therefore, post processing becomes essential for these electron beam melted (EBM-ed) Ti-6Al-4 V alloys. Being the most common technique to improve such parts, milling of Ti-6Al-4 V alloy is very challenging and resulting tool wear issues, due to its unique material properties. Thus, this paper presents a comprehensive study on the surface integrity of EBM-ed Ti-6Al-4 V parts processed by precision grinding and electropolishing, aiming to qualitatively and quantitatively clarify the interrelation between process parameters and processed surface quality. The surface and subsurface characteristics such as profile accuracy, surface roughness, microstructure, defective layer and residual stress before and after post processing were compared and evaluated. The results show that by precision grinding, the profile accuracy was improved from over 300 µm PV to 7 µm PV, while surface roughness (R_a) was reduced from 30 µm to about 2 µm. The layer with partially melt particles was removed, but introduced a deformed subsurface layer with more residual stress. Then by applying electropolishing, the residual stress was released and the deformed layer was removed. In addition, R_a was further reduced to 0.65 µm. The research can serve as a reference for the integration of post machining processes with AM.     

磁等离子体推力器工作机理与应用前景研究

研究了发动机能量输入、工质电离、等离子体加速及能量转换过程及机理,同时分析了磁等离子体推力器在空间推进任务中的应用前景.研究表明磁等离子体推力器主要利用电磁力加速和磁喷管的能量转换作用来实现加速,这种方式在大功率条件下,能够获得大推力、高功率和较长工作时间,在大功率轨道航天器和深空任务中有广阔的应用前景.     

METHIS: Mercury thermal infrared spectrometer

The BepiColombo mission to Mercury is devoted to the thorough exploration of Mercury and its environment, with the aim to understand the processes of planetary formation and evolution in the hottest part of the protoplanetary nebula. This mission represents an unique opportunity for the European community to extend the understanding of the Solar Nebula evolution from its outer edge – ideally represented by comets – to its inner and warmer edge. Obviously this exploration asks for a detailed knowledge of the main constituents of the matter present in the different Solar System areas. Spectroscopy is a powerful tool to acquire this knowledge. We have participated with a large consortium of European researchers to the development of the Rosetta imaging spectrometer. We propose here to use our experience to develop a newly designed spectrometer to investigate the mineralogical composition of the Mercurial surface. Given the particular thermodynamical situation of the Mercurial surface, we have developed a concept that combines a medium IR low spectral resolution imager with a moderate spectral resolution NIR point spectrometer. The main goal of METHIS is to provide the mineralogical characterisation of the surface with sufficient spectral resolution in a scientifically diagnostic spectral range.     

核热火箭发动机系统循环方案分析与设计

核热火箭发动机是未来实现载人火星探测的首选动力方案,其具备高比冲、大推力和长工作寿命等优点。我国在此方面研究较少,亟需开展核热推进技术理论及方法的研究。核热火箭发动机系统循环分析与设计是关键问题之一,对推进系统总体设计有重要意义。分析了3种可用于核热火箭发动机系统循环的方案特点,基于闭式膨胀循环设计了比冲为910 s ...     

一种基于自动相关信息四维运算的飞行间隔算法设计与实现

本文介绍了无人机（UAV：UnmannedAerialVehicle）航路规划的分层模式，提出了实时航路规划中四维接近算法，对UAV与静态和动态目标的接近距离进行了分析计算，为航路规划及时提供飞行过程中的危险接近信息，并进行了数字仿真。数字仿真表明：该算法具有较高的运算速度和较好预测精度，可快速提供UAV与周围静态和动...