Kevlar纤维表面改性对PA6/Kevlar纤维复合材料等温结晶行为的影响

用差示扫描量热仪(DSC)研究了KF表面阴离子接枝尼龙6对PA 6/KF复合材料等温结晶行为的影响。结果表明,PA 6的等温结晶过程主要为成核作用控制;未接枝的KF对PA 6结晶起异相成核作用,提高了PA 6的结晶速率;表面阴离子接枝尼龙6的KF对PA 6结晶仍起异相成核作用,但由于复合材料的界面相互作用提高,同时又会阻碍PA 6分子链的迁移运动,导致表面阴离子接枝PA 6的PA 6/KF复合材料中PA 6组分的结晶速率虽比纯PA 6大,但比未接枝PA 6的PA 6/KF复合材料小,且结晶度也有所下降。     

MACHINING OF TiB2 AND ITS COMPOSITES

The mechanism of material removal during electrical discharge machining (EDM) of TiB₂ and its composites was studied by examining surfaces and debris using electron microscopy and X-ray diffraction. In TiB₂, melting occurs due to formation of eutectic liquid with present impurities. In TiB₂-laminates melting and creation of high residual stresses produced cracks and fissures. The surface hardness was comparable to that obtained by polishing. During EDM of BN-TiB₂ composites, TiB₂ forms eutectic liquid at the interface with BN, and residual BN and some TiB₂ spall due to thermal shock. During pause periods parts of the liquid and fragments are flushed out by the dielectric. Composites rich in TiB₂ or with fine TiB₂ grains gave high material removal rates due to their high electrical conductivity. For all BN-TiB₂ composites, the diamond saw yielded much higher material removal rates than EDM but, unlike EDM, the diamond saw gave relatively lower removal rates for compositions rich in TiB₂, and for composites with fine TiB₂ grains due to their high hardness.     

SURFACES OF ADVANCED CERAMIC COMPOSITES FORMED BY ELECTRICAL DISCHARGE MACHINING

Ceramic composites shaped by electrical discharge machining were examined by several analytical techniques, including scanning electron microscopy, XPS, elemental distribution maps, and hardness testing, to determine changes due to EDM and to compare these surfaces to those obtained by other machining methods. Preferential oxidation was observed for some composites, while others showed no chemical changes. Correlations for material removal rate, surface roughness, and diameter to depth ratio for the crater were developed.     

A CRITICAL STUDY ON MACHINING OF Al/SiC COMPOSITES

This study focused on the tool topography and chip formation during machining of aluminium-silicon carbide particulate composites. The Al/SiC composites with different volume fraction of reinforcements were machined with cemented carbide tool inserts. The effects of volume fraction, cutting speed, feed rate, depth of cut, and time of machining on chip disposability, chip thickness ratio, and shear angle were studied. The quick-stop sections and chip cross sections at different conditions were also observed. The tool topography was also analyzed.     

Kevlar纤维增强尼龙6复合材料的界面结晶效应

采用阴离子接枝法对Kevlar纤维（KF）进行改性.利用偏光显微镜研究了未改性Kevlar纤维（KF0）和改性Kevlar纤维（KF1）增强尼龙6复合材料的结晶情况,界面横晶的形成机理及影响因素.结果表明,在尼龙6/ KF复合体系中,KF0和KF1的加入都能诱发其表面的基体PA6形成横晶,在低温下纤维的诱发横晶能力小,形成的横晶不致密、不完整;在高结晶温度Tc下形成的横晶完整而致密,纤维的诱发横晶能力大;KF1与基体有较强的结合力,故其诱发横晶能力较KF0强。     

FABRICATION AND CHARACTERIZATION OF Cu-SiCp COMPOSITES FOR ELECTRICAL DISCHARGE MACHINING APPLICATIONS

Cu-SiC_p composites made by the powder metallurgy method were investigated. To avoid the adverse effect of Cu-SiC_p reaction, sintering was controlled at a reaction temperature less than 1032 K. Electroless plating was employed to deposit a copper film on SiC_p powder before mixing with Cu powder in order to improve the bonding status between Cu and SiC particles during sintering. It was found that a continuous copper film could be deposited on SiC_p by electroless copper plating, and a uniform distribution of SiC_p in Cu matrix could be achieved after the sintering and extrusion process. The mechanical properties of Cu-SiC_p composites with SiC_p contents from 0.6 to 10 wt% were improved evidently, whereas electrical properties remained almost unchanged as compared with that of the pure copper counterpart. In the electrical discharge machining (EDM) test, the as-formed composite electrodes exhibited a character of lower electrode wear ratio, justifying its usage. The optimum conditions for EDM were Cu-2 wt% SiC_p composite electrode operating with a pulse time of 150 μsec.     

尼龙6/Kevlar纤维复合材料的非等温结晶行为及熔融特性

采用阴离子接枝法对K ev lar纤维(KF)进行表面改性,并用挤出方式分别制备尼龙6/未改性K ev lar纤维(PA 6/KF 0)及尼龙6/改性K ev lar纤维(PA 6/KF 1)复合材料。利用差示扫描量热仪(DSC)研究了KF 0和KF 1对PA 6/KF复合材料非等温结晶行为与熔融特性的影响,并与PA 6进行比较。结果表明,KF 0和KF 1起成核作用,提高了基体PA 6结晶的起始温度Tconset,减小其总结晶时间ttotal,同时提高了PA 6熔融时低温峰的相对强度,其中KF 1的效果更为明显;随着冷却速率β的加快,PA 6/KF 0和PA 6/KF 1复合材料中PA 6组分与纯PA 6一样,其Tocnset移向低温,且PA 6的熔融热谱由单重熔融峰向双重熔融行为转变。     

Kevlar层合材料抗弹性能研究

以Kevlar纤维增强层合材料为对象,通过系列弹道冲击实验,研究了层合板的抗弹性能,着重分析了弹头、纤维铺设方式以及板厚等因素对靶板抗侵彻能力的影响,同时对靶板的破坏模式也作了必要的讨论.此外,还通过一种工程近似方法,分析了不同弹头弹丸的弹道极限速度,预测值与实验值具有良好的一致性.     

二氧化硅/ 聚酰亚胺纳米杂化薄膜室温及低温力学性能

利用溶胶-凝胶技术制备了不同SiO₂ 含量的二氧化硅/ 聚酰亚胺(SiO₂ / PI) 纳米杂化薄膜。采用红外光谱( IR) 和扫描电镜(SEM) 手段对该体系的分子结构和断裂形貌进行了表征, 研究了聚酰亚胺薄膜室温和低温(77K) 力学性能。结果表明: 室温和低温(77 K) 下, SiO₂ / PI 杂化薄膜的拉伸强度开始时均随SiO₂ 含量的增加而增加, 在含量为3 %时达到最大值, 低温下杂化薄膜的拉伸强度明显高于室温。室温下, 杂化薄膜的断裂伸长率在含量为3 %时达到最大值, 而低温(77 K) 下, 薄膜的断裂伸长率的变化没有呈现明显的规律性。      

空间低温光学试验深低温背景环境的实现

为了实现空间低温光学试验的深低温背景条件,对实现深低温环模技术以及氦冷却系统进行了探讨.通过分析得到以氦循环方式建立的20 K稳定深低温冷黑背景是最为合适的低温光学试验背景环境.该系统是由氦液化系统配合相应冷氦分配装置以及终端冷舱组成密闭循环系统.氦液化系统是基于由布雷顿循环和焦耳-汤姆逊作用组合而成的克劳德循环,它能持续提供一定流量和压力的液氦或冷氦气作为循环系统中制冷工质,从而为试验提供稳定的深低温环境.     

SiO2/环氧树脂基纳米复合材料的室温和低温力学性能

利用溶胶-凝胶法制备了SiO₂/环氧树脂基复合材料,研究了材料的室温与低温(77 K)下的力学性能。结果表明,适量SiO₂的引入提高了室温与低温下材料的拉伸强度、断裂伸长率和冲击强度,即SiO₂含量在2%时可同时起到增强、增韧作用。采用扫描电镜(SEM)和透射电镜 (TEM)分别对复合材料的断口形貌和高温焚烧后残留物纳米颗粒进行了观察。还利用动态力学分析(DMA)研究了二氧化硅的引入对复合材料的影响。      

低温容器的研制

着重介绍了低温高压液氢容器和全包式预冷夹套低温容器的结构，容器分为三导：外容器是真空容器，夹套容器是预冷介质容器，内容器是低温介质容器。容器可用液氮预冷，大大节省预冷液氢，全包式的预冷夹套液氢容器，使预冷夹套发挥最大作用，其关键是使用了锥筒式支承，锥筒小端支承在内容器颈管上，大端支承在外容器上，在内容器上没有任何支耳和凸台，透用于带预冷夹套低温容器和多层绝热低温容器。     

法兰密封的低温试验研究

在液氮液氦温度下对5种纯金属和4种法兰做密封性能试验,并对超流氦试验装置进行分析和介绍.     

THE LASER CUTTING OF KEVLAR: A STUDY OF THE CHEMICAL BY-PRODUCTS

Several Kevlar (poly (p-phenylene terephthalamide), a product of E.I. Du Pont, Inc.) composites were cut with a CO₂ laser at a rate of 150 inches per minute and 1.0 kwatt of power (approximately 4.9×10⁵ watts/cm²). Atmospheric samples of the chemical by-products formed during the laser cutting were collected and analyzed by gas chromatography (GC), gas chromatography/massspectroscopy (GC/MS), and high pressure liquid chromatography (HPLC). A number of toxic and cancer-producing compounds were identified in the smoke plume produced; therefore, appropriate ventilation must be provided to insure the health and safety of personnel working in laser facilities processing Kevlar containing products.     

冷氦压力调节器的研制

长三甲火箭在国内率先采用了冷氦增压系统，冷氦压力调节器是冷氦增压系统中的最关键阀门之一。本文介绍冷氦压力调节器的方案，原理及形成过程。叙述了研制中解决的几个关键技术问题。整理出恒压加载式压调器的设计步骤，推导了设计计算公式。     

低温流体的空间输送技术

介绍了美国宇航局刘易斯研究中心有关低温流体空间输送方面的最新研究情况，包括设备研制、实验结果、新方案和新技术等。描述了低温流体空间输送技术的效益；最后讨论了这些技术的改进与发展。     

低温氦气体轴承透平膨胀机的设计

针对我国氦透平膨胀机的研制任务，设计了一台氦气体轴承透平膨胀机。从机械性能方面就该氦透平膨胀机开展了理论与试验研究，以高稳定性为主要目标进行了氦透平膨胀机的结构设计，实现了绝热及密封、快速装拆等要求。氦透平常温、低温实验证明该机具有良好的热力性能及机械性能，本文侧重于对该氦透平膨胀机结构设计的探讨。     

橡胶低温冲击断裂机理研究

基于橡胶单颗粒低温冲击破碎的实验研究，本文对橡胶低温冲击断裂机制进行了研究，首先对高聚物的力学特性作了必要的讨论，确定橡胶单颗粒冲击破碎的应力类型，建立了高聚物球形颗粒冲击破碎过程中应力波的传播模型，利用扫描电子显微镜对实验所得破碎颗粒的断面进行微观形貌观察，将观察结果与该模型比较，验证了模型的正确性。     

新型低温温度传感器的研制

对几种新型的低温温度传感器技术做了简单的介绍，研制了新型的低温温度传感器并做了大量的试验。试验结果表明，这几种传感器可以替代热敏电阻和热电偶传感器在火箭发动机试验中的应用，其精度、稳定性、互换性、自热效应等特性都优于热敏电阻和热电偶传感器。     

低温容器应用进展及发展前景（一）

综述了低温容器在航天、航空、机械、电子、地质矿产、冶金、建设、环保、交通、农业、卫生、食品、能源、化工、科技等部门的应用现状,展望了未来发展前景。