在轨维修后端模块接口机构的研究

在轨维修可以大大的延长空间科学仪器的使用寿命,节省大量的经济成本。为了实现空间望远镜后端模块的在轨操作和更换,设计了一套与之对应的接口机构,能够解决在轨快速定位与安装。根据321运动学定位准则,详细介绍了该接口机构的内部组成和工作原理;然后把该接口机构与后端模块进行组件级有限元仿真,仿真结果表明一阶模态远高于整机基频可以有效地避免发射时候的共振;设计了一套平面内的工装来模拟后端模块,利用等效质量法对整个机构进行重力卸载;搭建实验平台,利用激光跟踪仪来测量整个后端模块的重复定位安装精度,实验数据表明,X,Y,Z 3个方向的重复平移定位误差分别为±5.58μm,±3.24μm及±3.63μm,优于总体指标±10μm;热实验结果表明整个机构可以完全释放由于温度变化产生的形变,具有很高的热稳定性;使入射光线和靶面的相对位置持续稳定,保证了较高的成像质量。为其他空间在轨维护装置提供强有力的参考价值。     

CFD modeling of thermal contact resistance between solid contacting surfaces

Heat transfer has considerable applications in different industries such as designing of heat exchanger, nuclear reactor cooling, control system for spacecraft, and designing of microelectronics cooling. As the surfaces of two metals contact each other, this issue becomes so crucial. Thermal contact resistance (TCR) is one of the key physical parameters in heat transfer of mentioned surfaces. Measuring the experimental value of TCR in laboratory is highly expensive and difficult. As an alternative, numerical modeling methods could be engaged. In this study, inverse problem method solution is utilized as a proper method for estimation of TCR value. In this order, three different configurations (flat-flat, flat-cylinder, and cylinder-cylinder) were utilized in two steady and unsteady state conditions to predict the value of TCR. A comparison between the measured values and obtained values from the simulation show the errors for flat-flat, flat-cylinder, and cylinder-cylinder configuration after 10 min from starting the experiment are 4.6074%, 0.1662%, and 0.5622%, respectively. And in steady-state condition, the corresponding errors are 6.06e-3%, 1.506%, and 0.846%, respectively. In conclusion, the final results establish the fact that the inverse problem method solution can predict TCR values between contacting surfaces.     

Impact of adhesive ingredients on adhesion between rubber and brass-plated steel wire in tire

Proficiency on underlying mechanism of rubber-metal adhesion has been increased significantly in the last few decades. Researchers have investigated the effect of various ingredients, such as hexamethoxymethyl melamine, resorcinol, cobalt stearate, and silica, on rubber-metal interface. The role of each ingredient on rubber-metal interfacial adhesion is still a subject of scrutiny. In this article, a typical belt skim compound of truck radial tire is selected and the effect of each adhesive ingredient on adhesion strength is explored. Out of these ingredients, the effect of cobalt stearate is found noteworthy. It has improved adhesion strength by 12% (without aging) and by 11% (humid-aged), respectively, over control compound. For detailed understanding of the effect of cobalt stearate on adhesion, scanning electron microscopy and energy dispersive spectroscopy are utilized to ascertain the rubber coverage and distribution of elements. X-ray photoelectron spectroscopy results helped us to understand the impact of Cu_XS layer depth on rubber-metal adhesion. The depth profile of the Cu_XS layer was found to be one of the dominant factors of rubber-metal adhesion retention. Thus, this study has made an attempt to find the impact of different adhesive ingredients on the formation of Cu_XS layer depth at rubber-metal interface and establish a correlation with adhesion strength simultaneously.     

基于涡动相关法的沉积物-水界面氧通量与水动力条件响应关系

沉积物-水界面是物质参与环境地球化学循环和生物耦合的"热区",水动力条件是沉积物-水界面物质交换的关键影响因素。溶解氧作为常用的水质评价指标,对调节生物化学进程有重要作用,因此本文采用涡动相关法这种非侵入式通量测量技术开展室内试验研究,探究沉积物-水界面氧通量与水动力条件的响应关系。结果表明:随着水体紊动增加(采用Batchelor尺度表征),扩散边界层厚度减小,氧通量增大。分析室内试验和相关研究中水动力条件、扩散边界层厚度及氧通量的关系,发现扩散边界层厚度与Batchelor尺度呈正相关关系,拟合结果表明可以用Batchelor尺度近似表示扩散边界层厚度;氧通量与扩散边界层厚度呈负相关关系,且当扩散边界层厚度小于0.5 mm时,扩散边界层厚度变化对氧通量影响更强烈,当厚度大于0.5 mm后,氧通量基本保持稳定。     

工艺参数对6061-T6铝合金真空扩散焊接接头形貌和性能的影响

在不同工艺参数下对化学清洗去除表面氧化膜的6061-T6铝合金进行真空扩散焊接,研究了焊接温度(500~560℃)、焊接压力(1.0~5.0MPa)和保温时间(0.5~3h)对焊接接头界面形貌和剪切强度的影响,得到了优化工艺参数。结果表明:随着焊接温度的升高、焊接压力的增大和保温时间的延长,接头焊缝变窄并最终消失,剪切强度和焊合率增大;但当保温时间延长到3h时,焊缝附近晶粒发生粗化,导致剪切强度降低,且接头发生较大变形;不同工艺参数下接头的剪切断裂形式均为脆性断裂;较优的真空扩散焊接工艺参数为焊接温度540℃、保温时间2h、焊接压力4.0MPa。     

Influence of Y2O3 addition on the mechanical and oxidation behaviour of carbon fibre reinforced ZrB2/SiC composites

The influence of Y₂O₃ addition on the microstructure, thermo-mechanical properties and oxidation resistance of carbon fibre reinforced ZrB₂/SiC composites was investigated. Y₂O₃ reacted with oxide impurities present on the surface of ZrB₂ and SiC grains and formed a liquid phase, effectively lowering the sintering temperature and allowing to reach full density at 1900 °C. The presence of a carbon source (fibres) led to additional reactions which resulted in the formation of new secondary phases such as yttrium boro-carbides. Mechanical properties were significantly enhanced compared to the un-doped composite. Further tests at high temperatures resulted in strength increase up to 700 MPa at 1500 °C which was attributed to stress relaxation. Oxidation tests carried out at 1500 °C and 1650 °C in air showed that the presence of the Y-based secondary phases enhanced the growth of ZrO₂ grains, but offered limited protection to oxygen due to the lower availability of surficial SiO₂ formed from SiC.     

轧制速度对AZ31镁合金管材冷轧成形的影响

轧制速度是三辊式冷轧成形过程中关键的工艺参数，决定其力学特征及温升情况。基于此，本文以冷轧AZ31镁合金管材为研究对象，通过全流程数值仿真计算，对比分析不同轧制速度在各特征变形段对等效应力、等效塑性应变及节点温度的影响规律。结果表明，等效应力、等效塑性应变及节点温度均随轧制速度的增大而增大。通过元胞自动机模型及实验等手段，探明了晶粒在轧制过程中产生连续再结晶并细化的初步组织演变规律；对比分析实验与模拟结果并结合多方面因素，得到800mm/s的轧制速度可以更好的满足工艺要求的结果，为冷轧镁合金管材轧制速度的选择提供依据。     

絮体表面形态对膜污染预测的影响

现有对混凝-膜过滤过程中膜污染的预测分析，一般采用XDLVO理论对光滑界面的作用能进行计算，但混凝絮体表面形态会对预测结果产生较大的影响。利用正弦波球体模型对粗糙腐殖酸(HA)絮体表面进行模拟，并通过表面元素积分法(SEI)结合XDLVO理论与复合辛普森规则，对不同粗糙程度的混凝絮体与聚偏氟乙烯(PVDF)膜的界面作用能进行量化模拟；并将结果与传统XDLVO理论模拟的光滑界面作用能进行了比较。实验结果表明，该模型适用于混凝-膜过滤体系中絮体界面作用能的模拟，同时在模拟过程中，由于粗糙度的不同会导致界面作用能在数值上存在1~2个数量级的差异；并且粗糙的絮体较完全光滑的絮体与膜污染趋势的拟合程度更高，即引入絮体表面形态对利用絮体与膜界面间相互作用能表征膜污染趋势的置信度更高。     

Rice spike-like g-C3N4/TiO2 heterojunctions with tight-binding interface by using sodium titanate ultralong nanotube as precursor and template

A novel rice spike-like g-C₃N₄/TiO₂ nanowire heterojunctions are fabricated by hydrothermal treating Na₂Ti₃O₇ ultralong nanotubes in the presence of g-C₃N₄. The presence of g-C₃N₄ promotes the hydrolysis of Na₂Ti₃O₇ ultralong nanotubes. The partially replaced O of TiO₂ by N from g-C₃N₄ leads to the formation of a tight-binding interface between one dimensional TiO₂ and two dimensional g-C₃N₄, which is crucial for fast and effective transfer of photogenerated electrons in heterostructured photocatalysts. As a result, the g-C₃N₄/TiO₂ nanowire heterojunctions exhibit excellent visible-light photocatalytic activity. The kinetic constant (k) of g-C₃N₄/TiO₂ (0.024?min^?1) for degradation of methylene blue under visible light irradiation is 1.85 and 4 times than that of pure g-C₃N₄ and P25, respectively.