巨磁电阻材料(La1-xGdx)2/3Ca1/3MnO3的制备工艺及其结构研究

采用固相反应法制备巨磁电阻材料(La1-xGdx)2/3Ca1/3MnO3和La1-xZnxMnO3.La2/3Ca1/3MnO3样品在1200～1400 ℃等五个不同温度下烧结12h;(La1-xGdx)2/3Ca1/3MnO3(x=0.2,0.4,0.6,0.8,1.0)样品系列在1350℃下分别烧结12h和24h,另外样品La1-xZnxMnO3(x=0.1,0.5,0.9)系列在1350℃下烧结24h.利用X射线衍射(XRD)和扫描电镜(SEM)对各样品晶体结构和表面微观结构进行了研究.X射线衍射结果表明,所有样品晶体结构基本不变,保持钙钛矿结构(空间群为Pnma),但随着掺杂量的增加,样品(La1-xGdx)2/3Ca1/3MnO3和La1-xZnxMnO3系列的晶格常数和晶胞体积发生了变化,并且产生了杂质相,导致对结构很敏感的这些材料的磁电性能发生变化.扫描电镜结果表明,样品La2/3Ca1/3MnO3在1400℃时烧结效果最好.     

ZnMnO3及LaZnMnO3的制备及结构特性

对ZnO与MnO2固相反应进行研究,当烧结温度超过1300℃和烧结时间超过12h,ZnO与MnO2固相反应生成ZnMnO3的四面体结构.对La1-xZnxMnO3材料的制备条件进行研究,对结构进行表征.研究结果表明,固相反应只与烧结温度和烧结时间有关,与压制压力没有太大关系.当烧结温度超过1300℃和烧结时间超过6h,X射线衍射谱表明都具有钙钛矿衍射峰,但掺杂浓度在50%～70%时有新的衍射峰,可能产生了新相,有待进一步深入研究.     

钙钛矿型La_(1-x)Ba_xMnO_3(0≤x≤0.5)的红外发射率和微波吸收性能

通过溶胶凝胶法制备钙钛矿结构的La_(1-x)Ba_xMnO_3(0≤x≤0.5),利用X射线衍射、四探针电阻测量仪、红外发射率测试仪、矢量网络分析仪分别研究Ba~(2+)掺杂对镧锰氧化物晶体结构、电阻率、红外发射率和微波吸收性能的影响。研究结果表明:当Ba~(2+)掺杂浓度比较低时,掺杂的元素几乎不改变镧锰氧化物的晶体结构;当掺杂浓度增加时,晶格畸变开始增大;样品红外发射率随Ba~(2+)离子掺杂浓度的增大先降低后缓慢增加,与电阻率的变化保持一致;Ba~(2+)离子可以对样品在2~18 GHz微波吸收性能进行调控,当掺杂浓度x=0.3时,样品的吸收效果最佳;在频率为10.8 GHz时,最低反射率为-32 d B;掺杂合适元素的镧锰氧化物材料有可能应用在红外/雷达兼容隐身领域。     

BiFeO_3掺杂K_(0.5)Na_(0.5)NbO_3-LiSbO_3无铅压电陶瓷的相变及退极化性能研究

采用传统陶瓷常压烧结工艺,制备了BiFeO3掺杂0.95K0.5Na0.5NbO3-0.05LiSbO3(0.95KNN-0.05LS)无铅压电陶瓷,研究了该陶瓷的相转变、热滞与退极化性能。未掺杂和掺杂0.4mol%BiFeO3的0.95KNN-0.05LS陶瓷在室温下分别为正交相结构和正交相与四方相共存结构。掺杂后的陶瓷样品具有明显的热滞现象,热滞的温区约为300～380℃,对应陶瓷四方相与立方相共存的温区。所有陶瓷样品的平面机电耦合系数kp随温度的升高均减小,在300℃以下均有kp≥0.30。掺杂与未掺杂的KNN-LS陶瓷的退极化温度分别为360℃和370℃。     

电子束物理气相沉积Nd2O3和Yb2O3共掺杂的YSZ热障涂层研究

采用固相烧结的方法制备了10 mol% Nd2O3和Yb2O3共掺杂的YSZ(3.5 mol% Y2O3部分稳定的ZrO2)材料.掺杂材料为t/t'相,而8YSZ则为t/t'与m的混合相.测试结果表明:1 100 ℃时掺杂材料的热扩散系数为4.10×10-7 m2/s,而8YSZ(8 wt.% Y2O3部分稳定的ZrO2)的则为6.41×10-7 m2/s.在200～1 300 ℃温度范围内,掺杂材料的比热容均大大低于8YSZ.电子束物理气相沉积的掺杂材料的热障涂层陶瓷层为树枝晶结构.1 100 ℃下,掺杂材料的热障涂层热循环寿命为350～500 h,而同等条件下8YSZ涂层仅为160～200 h.     

铌酸锶钡陶瓷的固相烧结行为与结构演化研究

采用不同前驱体:Sr(NO3)2,Ba(NO3)2,Nb2O5(NSBN70)和SrCO3,BaCO3,Nb2O5(CSBN70)用传统烧结方法制备Sr0.7Ba03Nb2O6陶瓷.通过XRD、SEM实验手段,研究了硝酸盐前驱体制备过程中烧结温度和烧结时间对结构演化的影响.对比了不同前驱体制备SBN70陶瓷的显微结构.实验结果显示:采用硝酸盐前驱体,1400℃下烧结4h可得到纯SBN70相;1375℃烧结6h得到纯SBN70相.与碳酸盐前驱体相比,NSBN70呈现出双结构,比CSBN70易于出现异常晶粒长大.     

Yb3+、Er3+共掺杂Sm2Zr2O7陶瓷导热性能研究

为探究在Sm₂Zr₂O₇中A位掺杂Yb³⁺和Er³⁺对其导热性能的影响,采用固相合成法制备(Sm_1–x–yYb_xEr_y)₂Zr₂O₇(x=0.05,0.1;y=0,0.1)陶瓷材料,并对其物相结构及热物理性能测试。研究发现,改性后的(Sm_1–x–yYb_xEr_y)₂Zr₂O₇陶瓷材料为立方烧绿石结构。由于质量差和半径差的变化,声子散射增强,平均自由程减小,热导率降低,在600℃下,(Sm_0.85Yb_0.05Er_0.1)₂Zr₂O₇的热导率为1.3 W/(m·K),Yb³⁺     

双陶瓷层热障涂层3.5％Y2O3-La2(Zr0.7Ce0.3)2O7/YSZ研究

采用EB-PVD沉积了3.5％Y2O3-La2(Zr0.7Ce0.3)2O7(3.5Y-LZ7C3)/YSZ双陶瓷热障涂层,分析了涂层的成分、相结构、组织形貌和热循环氧化性能.研究表明:La2(Zr0.7Ce0.3)2O7(LZ7C3)材料中掺杂Y2O3能有效地降低涂层中La2O3/ZrO2/CeO2的成分偏差;双陶瓷涂层在1050℃下氧化增重动力学为M=0.1219t1/3,相比抛物线型YSZ涂层的氧化增重曲线,较大减缓了氧化速度;沉积态双陶瓷涂层表面结构(即3.5Y-LZ7C3涂层结构)为烧绿石结构,经过热循环后逐渐分解,出现了萤石结构以及La2O3的衍射峰;在1050℃双陶瓷层热循环氧化寿命达768h.     

Co/NM/FM(NiFe and Co)纳米多层膜的层间耦合效应

巨磁电阻自旋阀多层膜作为磁敏传感器材料与磁随机存储器(MRAM)材料，具有高的可靠性与灵敏度，在航空航天等高科技领域有着极大的应用前景。研究多层膜各层间的耦合效应与各层厚度、磁学性能之间的内在关系，对提高自旋阀的巨磁电阻效应、磁灵敏性等具有重要的作用。本研究采用磁控溅射沉积制备了(Cu／Co、Cu／NiFe，Ta／NiFe双层膜与Co／Cu／Co、Co／Cu／NiFe、Co／Ta／NiFe)三明治结构薄膜。采用振动样品磁强计对薄膜磁性、四探针法对薄膜磁阻性能进行了测试研究，采用洛仑兹电子显微镜法观察了薄膜的磁畴结构。研究结果表明，层间耦合效应不仅与非磁性中间层的厚度相关，而且与中间层材料的特性相关。磁阻与磁畴观察均表明层间耦合效应随中间层厚度的增加而减小，而Cu作为中间层的多层膜的层间耦合大于Ta作为中间层的层间耦合。     

MA 及原位-热压合成TiC/ Ti5 Si3 复合材料

以Ti粉、Si粉和C粉为原料,利用高能球磨及热压工艺合成了TiC/Ti5Si3陶瓷复合材料。研究了工艺条件尤其是热压温度对合成产物相组成及微观结构的影响,并结合DSC、XRD和SEM对反应合成机理进行探讨。结果表明:通过优化合成工艺,高能球磨12 h,热压温度1 400℃时,烧结6 h得到了高纯度的TiC/Ti5Si3陶瓷复合材料;合成过程为:反应开始时发生Ti+C■TiC,反应ΔG=-167.72 kJ/mol。2 h时发生5TiC+8Si■Ti5Si3+5SiC,反应ΔG=-62.12 kJ/mol,当6 h时发生3SiC+8Ti■Ti5Si3+3TiC,反应ΔG=-697.8 kJ/mol。显微结构表明:TiC/Ti5Si3复合材料的合成过程伴随Si熔融,该材料以TiC-Si-Ti5Si3形式相结合,其中Si为黏结剂。     

有翼高超声速再入飞行器气动设计难点问题

有翼高超声速再入飞行器是近年来的研究热点,气动设计是飞行器设计的关键。为了更清楚地认识有翼高超声速再入飞行器气动设计的难点问题,对有翼高超声速再入飞行器的发展、优势及总体任务剖面进行了介绍,从5个方面详细介绍了该类飞行器气动设计的难点问题,包括多约束复杂面对称气动布局设计、高温真实气体效应对气动特性影响、天地差异与天地换算方法、反作用控制系统(RCS)喷流干扰对气动特性的影响以及气动数据不确定度等,简要阐明了这些难点问题对总体设计的重要性以及初步的解决思路,为有翼高超声速再入飞行器气动设计提供了一些参考。     

Simulation and Analysis of Crashworthiness of Fuel Tank for Helicopters

Crashworthiness requirement of fuel tanks is one of the important requirements in helicopter designs. The relations among the protection frame, textile layer and rubber layer of the fuel tank are introduced. Two appropriate FE models are established, one is for an uncovered helicopter fuel tank without protection frame, and the other is for fuel tank with protection frame. The dynamic responses of the two types of fuel tanks impinging on the ground with velocities of 17.3 m/s are numerically simulated for the purpose of analyzing energy-absorbing capabilities of the textile layer and protection frame. The feasibility of the current crashworthiness design of the fuel tank is examined though comparing the dynamic response behaviors of the two fuel tanks.     

The effect of inlet conditions on the flow and heat transfer in multiple rotating cavity with axial throughflow

This paper discusses experimental results from two different build configurations of a heated multiple rotating cavity test rig.Measurements of heat transfer from the discs and tangential velocities are presented.The test rig is a 70% full scale version of a high pressure compressor stack of an axial gas turbine engine.Of particular interest are the internal cylindrical cavities formed by adjacent discs and the interaction of these with a central axial throughflow of cooling air.Tests were carried out for a range of non-dimensional parameters representative of high pressure compressor internal air system flows(Re up to 5×106 and Rez up to 2×105).Two different builds have been tested.The most significant difference between these two build configurations is the size of the annular gap between the(non-rotating) drive shaft and the bores of the discs.The heat transfer data were obtained from thermocouple measurements of surface temperature and a conduction solution method.The velocity measurements were made using a two component,LDA system.The heat transfer results from the discs show differences between the two builds.This is attributed to the wider annular gap allowing more of the throughflow to penetrate into the cavity.There are also significant differences between the radial distributions of tangential velocity in the two builds of the test rig.For the narrow annular gap,there is an increase of non-dimensional tangential velocity V/Ωr with radial location to solid body rotation V/Ωr=1.For the wider annular gap,the non-dimensional velocities show a decrease with radial location to solid body rotation.      

突破技术趋同，波音再现竞争优势

 波音公司面临着来自空客公司的巨大挑战,企业战略性创新才是公司成功的关键。为此波音公司的全部战略性研究集中在扩大产品的差异性上,体现在3个方面：电子化（e-Enabled）运营环境、整体复合材料机身部件的制造技术和支持波音787客机的全球协同环境（GCE）。     

临近空间飞行器测控与信息传输系统频段选择

 临近空间飞行器是高性能信息化武器平台,测控（TT&;C）与信息传输系统是其信息保障的核心,而选择合理、可行的频段是展开系统设计的前提和基础。频段选择影响到整个技术方案的制定,是一个需综合考虑、影响深远并具有战略意义的关键问题,从国际电联（ITU）国际标准、高速数传、接收信噪比（SNR）、“三抗”、超视距中继、黑障、雨衰以及设备研制成熟度8个方面全面、细致论证了近空间平台测控系统的频段选择问题,最终得出在视距链路中以Ka频段为宜,在超视距链路中以Ku/Ka双频段为宜的结论。     

基于弯曲激波压缩系统的高超声速进气道反设计研究进展

总结了近十年来弯曲激波压缩研究的主要成果。提出了弯曲激波压缩系统的新概念,即利用特殊设计的楔形弯曲压缩面或空间弯曲压缩面,产生一系列与前缘弱激波相互交汇或叠加的压缩波系,从而使前缘激波弯曲,形成特殊的弯曲激波,它与波后的等熵压缩波来共同完成对气流的压缩。在此基础上,实现了由给定出口气动参数的超声速内流道反设计,实现了由给定压缩面压力分布和给定压缩面马赫数分布要求的型面反设计,实现了由给定激波波面的压缩型面反设计。研究证明,弯曲压缩面-弯曲激波压缩系统具有良好的综合气动性能,为高性能高超声速进气系统的气动设计提供了一种全新的设计方法。     

Experimental Study on Effects of Fuel Injection on Scramjet Combustor Performance

In order to investigate the effects of fuel injection distribution on the scramjet combustor performance, there are conducted three sets of test on a hydrocarbon fueled direct-connect scramjet test facility. The results of Test A, whose fuel injection is carried out with injectors located on the top-wall and the bottom-wall, show that the fuel injection with an appropriate close-front and centralized distribution would be of much help to optimize combustor performances. The results of Test B, whose fuel injection is performed at the optimal injection locations found in Test A, with a given equivalence ratio and different injection proportions for each injector, show that this injection mode is of little benefit to improve combustor performances. The results of Test C with a circumferential fuel injection distribution displaies the possibility of ameliorating combustor performance. By analyzing the effects of injection location parameters on combustor performances on the base of the data of Test C, it is clear that the injector location has strong coupled influences on combus- tor performances. In addition, an inner-force synthesis specific impulse is used to reduce the errors caused by the disturbance of fuel supply and working state of air heater while assessing combustor performances.     

(高)超声速流动试验技术及研究进展

近年来,与高速飞行器相关的(高)超声速流动受到了极大的关注。这类流动所具有的非定常性、强梯度和可压缩性对试验方法和风洞设计技术提出了挑战。超声速纳米示踪平面激光散射(NPLS)技术是由作者所在团队研发的非接触光学测试技术。它能够以较高的空间分辨率来揭示超声速三维流场的一个瞬态剖面的时间解析的流动结构。介绍了NPLS技术以及基于NPLS开发的密度场测量、雷诺应力测量和气动光学波前测量等方法,并回顾了这些技术在超声速边界层、超声速混合层、超声速压缩拐角、激波/边界层相互作用和光学头罩绕流等流动中的应用,清晰地再现了边界层、混合层、激波等典型流场结构及其时空演化特性。另外,为了模拟和研究高空大气条件下边界层自然转捩和超声速混合层的转捩特性,介绍了高超声速静风洞、超-超混合层风洞的设计技术以及层流化喷管的设计方法。     

Research on Auto-detection for Remainder Particles of Aerospace Relay Based on Wavelet Analysis

Aerospace relay is one kind of electronic components which is used widely in national defense system and aerospace system. The existence of remainder particles induces the reliability declining, which has become a severe problem in the development of aerospace relay. Traditional particle impact noise detection (PIND) method for remainder detection is ineffective for small particles, due to its low precision and involvement of subjective factors. An auto-detection method for PIND output signals is proposed in this paper, which is based on direct wavelet de-noising (DWD), cross-correlation analysis (CCA) and homo-filtering (HF), the method enhances the affectiv-ity of PIND test about the small particles. In the end, some practical PIND output signals are analysed, and the validity of this new method is proved.