复合柔性结构航天器动力学建模研究

柔性航天器动力学建模的传统方法是采用混合坐标法,针对中心刚体带大型柔性附件类的航天器,这种方法在理论建模和工程应用方面都获得了极大的成功。在中心刚体加柔性附件类航天器柔性动力学研究成果基础上,通过计及柔性体与柔性体连接点间的复合位移变形,利用混合坐标法建立了复合柔性结构航天器动力学模型,其软件系统DASFA 2.0已初步用于工程分析设计。     

3D基底上碳纳米管场发射I-V特性建模与计算

利用有限元分析软件ANSYS分析了在平面上引入立体墙结构的阴极电场分布,给出了立体墙结构阴极表面的场强分布曲线,结合F-N方程计算了在立体结构上生长碳纳米管和平面型冷阴极上直接生长碳纳米管的电流密度,通过数值计算计算了总的场发射电流,结果表明,场发射电流随场强的变化非常大,立体墙结构型冷阴极场发射电流与平面型冷阴极发射电流相比,场发射能力得到极大的增强。     

冷阴极电离真空计校准方法研究

主要介绍了冷阴极电离真空计结构、工作原理及冷阴极电离真空计的校准方法和校准装置,并对校准数据进行了处理.由于冷阴极电离真空计为非线性真空计,通过比较,校准结果采用了校准曲线的方式,可提高校准的准确度,减小校准不确定度,保证真空测量的可靠性.     

新型单边复和型柔性铰链的柔度计算及其性能分析

 提出了一种新型柔性铰链——单边直圆导角复合柔性铰链,以卡氏第二定理为理论基础,推导了单边直圆导角复合型柔性铰链的柔度计算式．利用所得结果对实例进行柔度的理论计算,同时对其作限元分析,通过结果对比,验证了柔度计算式的正确性．同时对单边直圆导角复合柔性铰链的性能进行分析,分析了结构参数对其柔度性能的影响,通过与双边直圆导角复合柔性铰链比较,得出了单边直圆导角复合柔性铰链的转动能力、对载荷的敏感性均优于双边直圆导角复合柔性铰链,为柔性铰链在结构紧凑、大位移场合的工程应用提供了新的思路．     

碳纳米管冷阴极大电流发射机理的研究

本文对碳纳米管冷阴极的场致发射机理进行了理论和实验研究.研究发现,如果场致发射冷阴极的发射面积很小,有可能得到较大的发射电流密度.当发射面积增加时,冷阴极的平均发射电流密度迅速下降,很难得到大的束电流.研究表明,在碳纳米管冷阴极的场致发射现象中,边沿场的场致发射现象起着非常重要作用.如果仅仅增加发射面积,边沿发射电流增加不多,这导致了平均发射电流密度的下降.因此,在阴极结构中增加发射体的边沿,则可有效提高阴极的发射电流.     

NCG冷阴极规管放电性能的测试

在NCG冷阴极规管的研制工作中,精确测量真空度低于10~(-8)帕下的放电性能和起辉性能是一个关键的问题。利用了一台按国际标准ISO设计制造的比对系统满足了测量要求.首先介绍了比对测试系统的特点以及测试原理,然后根据测试结果给出了规管在压力下限的放电曲线和起辉性能.最后应用磁场和电场相匹配的原理,改进冷阴极规管的磁结构,使规管成本降低了30%—40%,有利于推广应用.     

冷阴极气体放电电子枪的研制

为了促进冷阴极电子束加工技术在国内的发展,在深入研究冷阴极电子发射机理基础之上,设计制造了一种自主知识产权的冷阴极气体放电电子枪,对该电子枪的结构、阴极功能及其参数、阳极功能及其参数、CST仿真软件确定聚焦线圈参数的方法进行了介绍.通过实验发现:每一种放电气体的最小“点火”电压与放电气体种类、气流量大小有关;氦、氩等纯...     

薄膜型冷阴极电子源发光器件延迟特性的分析

利用金刚石及其相关薄膜制作冷阴极电子源,以及这类电子源在平板显示器件上应用的研究,是真空电子领域中一个重要的研究课题.本文对已研制成功的薄膜型冷阴极电子源发光器件进行了响应延迟特性的研究.同时分析导致器件产生延迟响应的因素,提出相应的电路模型.由此模型得到的理论结果与实验结果相吻合.     

基于取向结构的聚合物基柔性力敏材料的研究进展

柔性力敏材料是可穿戴材料领域的重要基础材料。与未取向的复合材料相比,具有取向结构的柔性力敏材料拥有更加优异的电学、力敏性及力学性能。文中从制备方法的角度归纳了具有取向结构聚合物基柔性力敏材料的研究进展,包括阵列结构与柔性聚合物复合、静电纺丝法、定向冷冻法及电场取向等,并从形态、结构及电学、灵敏性和力学性能方面对取向结构进行了表征,最后展望了具有取向结构的柔性力敏材料的发展趋势。     

合成纤维复合夹层屏蔽结构改性及其电磁特性研究

提出具有复合介质夹层屏蔽结构模型的设想,利用铜箔-聚四氟乙烯为原材料,设计了单层屏蔽结构与复合夹层屏蔽结构的对比实验,测试了复合夹层屏蔽结构的电磁屏蔽效能增量,并用Ватолцн多层电磁屏蔽理论公式进行了验证。具有复合夹层屏蔽结构材料的电磁屏蔽效能明显优于单层屏蔽结构材料的电磁屏蔽效能。继而以涤纶无纺布、锦纶合成纤维为研究对象,采用电化学改性的方法,制备了具有复合夹层屏蔽结构的柔性电磁屏蔽材料。结果表明,通过对研究对象的选择和优化电化学改性的工艺,可以制备出1 MHz~1000 MHz入射电磁波频段范围内,满足不同要求的合成纤维复合夹层屏蔽结构改性材料,其SE值最高可达98 dB。     

短切炭纤维增强沥青基C/C复合材料的组织特征

利用新型、高效的模压半炭化成型工艺，在大气环境下制备出了短切炭纤维增强沥青基C／C复合材料制品，并借助光学显做镜和扫描电镜对其微观组织和断口形貌进行了观察。通过分析，解释了短切炭纤维增强沥青基C／C复合材料中炭纤维损伤的形成机制，提出了作为增强体相的短切炭纤维和焦炭颗粒与基体炭之间独特的界而结构模型。研究还表明：复合材料中明显存在着基体相和颗粒相一基体相的显微结构不仅呈层片状，而且层片状的结构好像数层桔子皮，将颗粒相包裹起来，这种“桔皮包裹”式的结构与炭纤维表面的POG结构基本相似。     

短切炭纤维增强沥青基C/C复合材料的力学性能

利用模压半炭化成型工艺在大气环境下制备出了短切炭纤维增强沥青基C／C复合材料（简称SCFRC）。研究了短切炭纤维的体积分数对SCFRC材料的体积密度和力学性能的影响规律。借助光学显微镜和扫描电镜对其微观组织和断口形貌进行了观察，分析了短切炭纤维对SCFRC材料的增强机制。结果表明，当短切炭纤维的体积分数由0％增大到11．8％时，SCFRC材料的力学性能随之呈线性增加；短切炭纤维增强SCFRC材料的机制主要有裂纹偏转效应、桥联效应以及脱粘和拔出效应。     

Hierarchical carbon nanostructure design: ultra-long carbon nanofibers decorated with carbon nanotubes

Hierarchical carbon nanostructures based on ultra-long carbon nanofibers (CNF) decorated with carbon nanotubes (CNT) have been prepared using plasma processes. The nickel/carbon composite nanofibers, used as a support for the growth of CNT, were deposited on nanopatterned silicon substrate by a hybrid plasma process, combining magnetron sputtering and plasma-enhanced chemical vapor deposition (PECVD). Transmission electron microscopy revealed the presence of spherical nanoparticles randomly dispersed within the carbon nanofibers. The nickel nanoparticles have been used as a catalyst to initiate the growth of CNT by PECVD at 600°C. After the growth of CNT onto the ultra-long CNF, SEM imaging revealed the formation of hierarchical carbon nanostructures which consist of CNF sheathed with CNTs. Furthermore, we demonstrate that reducing the growth temperature of CNT to less than 500°C leads to the formation of carbon nanowalls on the CNF instead of CNT. This simple fabrication method allows an easy preparation of hierarchical carbon nanostructures over a large surface area, as well as a simple manipulation of such material in order to integrate it into nanodevices.     

Kinetics of chemical vapor infiltration of carbon nanofiber-reinforced carbon/carbon composites

Preforms containing 0, 5, 10, 15 and 20 wt.% carbon nanofibers (CNFs) were fabricated by spreading layers of carbon cloth, and infiltrated by using the technique of isothermal chemical vapor infiltration (ICVI) at the temperature of 1100 °C under the total pressure of 1 kPa and with the flow of the mixture of propane/nitrogen in a ratio of 13:1. The infiltration rates increased with the rising of CNF content, and after 580 h of infiltration, the achievable degree of pore filling was the highest when the CNF content was 5 wt.%, but the composite could not be densified efficiently as the CNF content ranged from 10 to 20 wt.%. An analysis of the results, based on the effective diffusion coefficient and on the in-pore deposition rates, shows that the CNFs, due to their higher aspect ratio, accelerate overgrowth at pore entrances and thus lead to incomplete pore filling.     

软硬混编预制体增强沥青基4D-C/C材料的拉伸破坏行为

以X-Y平面依次铺设炭纤维束、Z向穿插炭棒的4D软硬混编为预制体,采用沥青液相常压、高压浸渍/炭化-石墨化循环致密工艺制备4D-C/C复合材料。通过该材料Z向(炭棒方向)的拉伸实验,测定其拉伸性能和力学行为,并采用SEM分析试样表面及断口形貌。结果表明:宏观上拉伸试样以炭棒整体拔出的形式破坏;细观尺度上,试样表面形成了与载荷方向垂直的贯穿性裂纹,裂纹以2 mm左右的距离呈等间距分布;材料进一步的破坏过程中,基体裂纹在X-Y向纤维束中呈线性扩展,快速分割了基体材料,使4D-C/C复合材料的拉伸破坏演变为1D-C/C复合材料的破坏模式,由于炭棒与基体炭界面结合弱,炭棒以拔出方式失效和破坏。     

Diamond formation on carbon/carbon composite

A carbon/carbon composite was used as substrate for low-pressure diamond deposition. To enhanced diamond nucleation on carbon/carbon composites, a total of ten surface preparation methods have been investigated. These methods involved the use of atomic hydrogen etching, mechanical polishing, sonication, or coating. Diamond nucleation was found to occur on either the defects of the carbon/carbon composite substrates or diamond particulate left on the substrates. The defects were created primarily by atomic hydrogen etching during the coating process. Seeding with diamond powders was performed by dip coating, sonication, or spray-coating processes. It was found that these seeding processes resulted in excellent nucleation of diamond.     

Graphitization behaviour of carbon fibre-glassy carbon composites

Carbon fibre-carbon composites were fabricated by aligning PAN-based carbon fibre unidirectionally in furfuryl alcohol resin char. The graphitization behaviour was investigated by an X-ray diffraction technique and by the measurement of magnetoresistance. The time-temperature superimposition study for interlayer spacing resulted in an activation energy of 242±35 kcal mol⁻¹. The kinetic study on magnetoresistance agreed with the result of X-ray measurement. The activation energy is that for the graphitization of the layer structure formed in the glassy carbon matrix of the composites. The graphitization mechanism of the layer structure is the same as that of soft carbons.     

Mesoscale evolution of non-graphitizing pyrolytic carbon in aligned carbon nanotube carbon matrix nanocomposites

Polymer-derived pyrolytic carbons (PyCs) are highly desirable building blocks for high-strength low-density ceramic meta-materials, and reinforcement with nanofibers is of interest to address brittleness and tailor multi-functional properties. The properties of carbon nanotubes (CNTs) make them leading candidates for nanocomposite reinforcement, but how CNT confinement influences the structural evolution of the PyC matrix is unknown. Here, the influence of aligned CNT proximity interactions on nano- and mesoscale structural evolution of phenol-formaldehyde-derived PyCs is established as a function of pyrolysis temperature (\(T_{\mathrm {p}}\)) using X-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy. Aligned CNT PyC matrix nanocomposites are found to evolve faster at the mesoscale by plateauing in crystallite size at \(T_{\mathrm {p}}\) \(\sim\)800 \(^{\circ }\hbox {C}\), which is more than \(200\,\,^{\circ }\hbox {C}\) below that of unconfined PyCs. Since the aligned CNTs used here exhibit \(\sim\)80 nm average separations and \(\sim\)8 nm diameters, confinement effects are surprisingly not found to influence PyC structure on the atomic-scale at \(T_{\mathrm {p}}\) \(\le \)1400 \(^{\circ }\hbox {C}\). Since CNT confinement could lead to anisotropic crystallite growth in PyCs synthesized below \(\sim\)1000 \(^{\circ }\hbox {C}\), and recent modeling indicates that more slender crystallites increase PyC hardness, these results inform fabrication of PyC-based meta-materials with unrivaled specific mechanical properties.     

Development of vapor grown carbon fibers (VGCF) reinforced carbon/carbon composites

C/C composites are developed using vapor grown carbon fibers (VGCF) with two types of pitches as matrix precursor. The composites are carbonized at 1000°C by applying the isostatic pressure throughout the carbonization process and further heat treated at different temperatures up to 2500°C in the inert atmosphere. By applying iso-static pressure one can able to developed VGCF based C/C composites possessing the very high bulk density (1.80 g/cm³) and apparent density (2.01 g/cm³) only by heat treatment up to 2500°C without any densification cycle. This high value of density is due to the extremely strong fiber-matrix interactions and self sintering between the VGCF fibers during carbonization process under iso-static pressure. From the SEM study it reveals that, fiber-matrix interactions are strong and fiber boundaries merges with each other, also there is not a evidence of matrix shrinkage cracks in case 1500°C heat treated composites. On the other hand, in 2500°C heat treated composites, there is evidence of uniform fiber-matrix interfacial cracks and porosity in nanometer dimensions. This is due to the change in fiber morphology above HTT 1500°C. But the formation of nano width cracks does not affect on the mechanical properties of composites. The compressive strength increases from 95MPa of 1500°C to 105 MPa of 2500°C heat treated composites. However, hardness decreases due to the increase in the degree of graphitization of composites on 2500°C. The study reveals that by controlling processing condition and the uniform dispersion of VGCF fibers in the matrix phase, it can be possible to developed nano porosity at fiber-matrix interface.