基于标样比对测试的固体火箭发动机工业CT检测工艺

针对固体火箭发动机CT检测缺少行业标准的问题,使用正密度材料块模拟界面脱粘缺陷和使用合金块模拟药柱内部缺陷来制作标样发动机,对标样发动机和实际发动机进行CT检测对比试验,并解剖取样验证。结果表明发动机CT检测和射线照相、解剖试验结果吻合,标样发动机设计满足研究需要。同时确定了工业CT系统发现缺陷的最小能力:脱粘面积20 mm×20 mm,宽度0.4 mm,气孔和夹杂直径5 mm,裂纹宽度0.4 mm。建立检测标准规范了固体火箭发动机CT检测工艺。     

航空航天用铝合金机器人焊接内部气孔缺陷在线检测

铝合金机器人钨极氩弧焊(GTAW)是航空航天关键零部件的主要成形制造方法,内部气孔是其典型焊接缺陷。由于它与传感信息的弱相关性,实现准确的在线气孔检测仍极具挑战。利用SEM和EDS对气孔的宏观分布、成分含量及大小进行定性及定量表征,发现了两类内部气孔以及镁元素在气孔产生及长大过程中的重要性。利用主成分分析研究并建立了气孔与氢谱线(656.28nm)之间的强相关关系,提出了基于氢谱线主分量系数(PCoefHS)的气孔在线监测方法,最后通过集成PCA–Tsne技术对不同程度气孔缺陷进行可视化。验证结果表明所提方法可实现对严重链状气孔、中度气孔及无气孔缺陷焊缝的有效检测及可视化表征。     

复合材料修理结构的缺陷特征与超声信号

研究了热补仪修理复合材料层压板结构的缺陷特征。金相显微分析结果表明,当修补层数为2层时,样品没有任何缺陷产生;当修补层数增加到4层时,修补层内出现气孔缺陷;当修补层数增加到6层时,除了修补层内出现大量气孔缺陷以外,胶膜层也出现气孔,导致弱粘接/脱粘缺陷的产生。超声检测的结果与金相显微分析一致,很好地再现了上述缺陷。     

C_f/Al复合材料无损检测与质量评价初探

通过对Cf/Al复合材料进行X射线照相和超声波检测研究,实现对复合材料中的体积型缺陷(缩孔、疏松和气孔,纤维排布不均)和面积型缺陷(分层、纤维或集体聚集及垂直超声波声束方向裂纹)的检测,并逐步建立了缺陷检测和评价的暂行标准。     

含缺陷固体装药燃烧异常实验分析

利用高速实时Ｘ射线荧屏分析技术,对固体火箭发动机装药经常出现的主要缺陷导致的异常燃烧现象进行研究,提出了含不同类型缺陷装药结构破坏的条件和模式,描述了推进剂裂纹、气孔和脱粘槽穴内的点火、燃烧和结构变形现象,分析了双基、丁羟、ＮＥＰＥ推进剂裂纹进一步扩展趋势和临界条件,为评估固体发动机含缺陷装药燃烧安全性提供了实验依据和分析方法。     

固体发动机ICT断层图像去噪技术

由于受扫描电子设备、光电转换过程和重建算法的影响,固体发动机经ICT系统检测生成的灰度断层图像中含有多种噪声,严重影响了检测人员对发动机内部缺陷的诊断。为此,利用图像滤波技术对断层图像进行有效的处理,去除图像中的噪声,突出缺陷信息。在理论分析均值滤波、中值滤波、维纳滤波和小波变换滤波这4种滤波方法的基础上,分别将这4种方法应用到固体发动机ICT断层图像去噪中,经对比。得出维纳滤波在较好的保存缺陷信息的同时,有效的去除了噪声,是最适用于固体发动机缺陷检测需求的图像去噪方法。     

超声显微检测系统在涂层检测中的应用研究

主要介绍了超声显微检测系统的组成及原理，采用超声显微检测系统对特种涂层的内部质量进行了超声检测的应用研究。结果表明：该系统能检测出涂层内部的裂纹、气孔、涂层与基体脱粘等缺陷。采用超声瑞利波声透镜，可有效检测出涂层表面及亚表面的缺陷。检测过程中实时显示被测样品的A、B、C三种扫描图像，缺陷检测结果直观。     

固体火箭发动机衬层与药柱脱粘高能X射线检测技术

衬层与药柱脱粘严重影响固体火箭发动机的结构完整性和工作安全性,该缺陷的可靠检测至关重要。文章综述了固体火箭发动机高能X射线检测技术现状。基于射线照相检测和工业CT检测手段,评述了固体火箭发动机衬层与药柱脱粘的图像分析和缺陷评判技术。针对该类缺陷,提出了综合应用射线照相技术和工业CT技术进行印证检测的方法,评判结果表明能够满足缺陷检测的可靠性与准确性要求。     

气孔缺陷对TA15 钛合金氩弧焊接头疲劳性能的影响

对TA15钛合金氩弧焊接接头的组织和疲劳断裂特征进行了分析,对气孔缺陷和疲劳寿命的关系进行了定量表征.结果表明:疲劳裂纹起源于焊缝的亚表面或者内部气孔缺陷,当气孔尺寸较小时,断口会出现“鱼眼”形貌特征;应力水平较低时,气孔尺寸对疲劳寿命的影响尤为显著,在特定的应力水平下,可以通过构件中的气孔缺陷尺寸来预测其寿命,对于焊接结构疲劳寿命的预测和构件焊接质量的评定具有重要的工程意义.     

铝及其合金焊缝气孔的评价及其产生倾向——气孔对焊接接头性能的影响(1)

铝焊缝中产生的缺陷主要有气孔、未熔合、未焊透及裂纹等。与其它材料相比,铝板材料中气孔产生的频率最高,是典型的缺陷之一。气孔内的气体大部分是氢。气孔产生的原因之一是由于电弧周围呈熔化状态的铝对氢有     

Performance characteristics of lithium ion cells at low temperatures

The low temperature charge and discharge characteristics of experimental MCMB-Li/sub x/Ni/sub y/Co/sub 1-y/O/sub 2/ cells containing different electrolytes were investigated. The use of low ethylene carbonate (EC)-content electrolyte formulations has resulted in good discharge performance to temperatures as low as -40/spl deg/C. The effect of charge voltage and charge current upon the individual electrode potentials at low temperature was investigated using the three electrode cells (containing lithium reference electrodes). In some cases, lithium plating was observed to occur upon low temperature charge, and found to be facilitated by high charge voltages, high charge currents, and poor anode kinetics. Electrochemical characterization of the cells has helped to establish the conditions under which lithium plating can occur by providing information regarding the polarization effects present at each electrode.     

Effects of pore structure and distribution on strength of porous Cu-Sn-Ti alumina composites

Porous Cu-Sn-Ti alumina composites were fabricated by sintering Cu-Sn-Ti alloy powders, graphite particles, and alumina hollow particles agent. The effects of the pore structure and distribution on the composites strength were evaluated. Different pore distributions were modeled by using finite element analysis to investigate the tensile strength of the composites. Furthermore, a fractal analysis-based box-covering algorithm was used on the Cu-Sn-Ti alumina composites topology graphs to better investigate the pore structure and distribution. Results obtained show that different sizes and concentrations of alumina hollow particles could result in different porosities from20% to 50%. A larger pore size and a higher pore concentration reduce the strength, but provide more space for chip formation as a bonding material of a grinding wheel. The body-centered pore structure of the composites shows the highest stress under a tension load. The original composites topology graphs have been transformed to ordered distributed pore graphs based on the total pore area conservation. The information dimension magnitude difference between the original topology graphs and the ordered distributed circulars graphs is found to be linear with the Cu-Sn-Ti alumina composites strength. A larger difference renders a lower flexural strength, which indicates that uniform ordered distributed pores could benefit the composites strength.     

应用等离子体进行翼型升力控制的数值模拟研究

将等离子体对中性气体的作用模型化为彻体力矢量,求解带源项的Navier-Stokes方程,数值模拟了在NLF(1)-0213翼型上表面60%弦长处安装等离子体激励器对升力的控制效果.彻体力为净电荷在外加电场作用下的电场力.解拉普拉斯方程得到外加电场分布,等离子体中的净电荷分布由泊松方程给出.升力线计算结果与实验值吻合,激励器工作时,升力线向上平移,控制效果与襟翼类似.     

孔隙预置技术制备多孔C/SiC复合材料及其性能表征

以玻璃纤维为成孔剂,采用孔隙预置技术制备了发汗多孔C/SiC复合材料.对孔隙结构进行了表征,并研究了材料的力学性能和渗透行为.研究结果表明,采用孔隙预置技术能够有效地实现多孔 C/SiC材料开孔率和孔隙结构控制,该材料具有良好的力学性能和渗透性能.     

Ag/TiO2/ITO紫外探测器的制备及其光电性能

采用胶体晶体模板技术,结合磁控溅射工艺,制备出光电性能较为优异的 Ag反点阵列/TiO2/ITO三明治结构紫外探测器。通过扫描电子显微镜( SEM)、XRD、四探针测试仪及半导体参数测试仪对探测器的微观结构和光电性能进行了测试与表征。结果表明：反点阵列孔径对探测器光电性能影响较为显著;随着孔径增大,探测器的暗电流逐渐增大,光电流先增大后减小,响应时间逐渐延长;孔径为4.2μm时,探测器的光电性能达到最佳;孔径较大的反点阵列电极,具有较高的电导率、较低的紫外光透过率以及较大的光生电子-空穴的复合概率。     

Electric Charging and Discharging Processes of Moving Projectiles

Every type of missle is electrically charged during free flight. The physical mechanism, leading to the electric charging and discharging effects, was investigated by measuring the electric field surrounding projectiles while leaving the muzzle region, during free flight, and on impact on targets. The electric charge on projectiles is 10-13 108C. Numerous experimental results were obtained with calibers 4-155 mm and velocities 50-120lm/ s. A physical model about the complex charging effects is derived.     

X-ray and extreme ultraviolet emissions from comets

There is significant progress in the observations, theory, and understanding of the x-ray and EUV emissions from comets since their discovery in 1996. That discovery was so puzzling because comets appear to be more efficient emitters of x-rays than the Moon by a factor of 80 000. The detected emissions are general properties of comets and have been currently detected and analyzed in thirteen comets from five orbiting observatories. The observational studies before 2000 were based on x-ray cameras and low resolution (E/δE ≈ 1.5-3) instruments and focused on the morphology of xrays, their correlations with gas and dust productions in comets and with the solar x-rays and the solar wind. Even those observations made it possible to choose uniquely charge exchange between the solar wind heavy ions and cometary neutrals as the main excitation process. The recently published spectra are of much better quality and result in the identification of the emissions of the multiply charged ions of O, C, Ne, Mg, and Si which are brought to comets by the solar wind. The observed spectra have been used to study the solar wind composition and its variations. Theoretical analyses of x-ray and EUV photon excitation in comets by charge exchange, scattering of the solar photons by attogram dust particles, energetic electron impact and bremsstrahlung, collisions between cometary and interplanetary dust, and solar x-ray scattering and fluorescence in comets have been made. These analyses confirm charge exchange as the main excitation mechanism, which is responsible for more than 90% of the observed emission, while each of the other processes is limited to a few percent or less. The theory of charge exchange and different methods of calculation for charge exchange are considered. Laboratory studies of charge exchange relevant to the conditions in comets are reviewed. Total and state-selective cross sections of charge exchange measured in the laboratory are tabulated. Simulations of synthetic spectra of charge exchange in comets are discussed. X-ray and EUV emissions from comets are related to different disciplines and fields such as cometary physics, fundamental physics, x-rays spectroscopy, and space physics.This revised version was published online in July 2005 with a corrected cover date.     

动态结冰微观孔隙结构定量分析

过冷水撞击低温基底结冰是典型的动态过程,易形成气泡孔隙,这一孔隙结构是决定动态结冰热/力学特性的根本因素。针对动态结冰微观孔隙结构定量研究的不足,以风洞结冰显微图像为对象,采用前期提出的变分分割模型,建立了结冰图像孔隙提取方法;基于孔隙提取结果,系统分析不同结冰条件下的孔隙形态、孔径分布等相关结构特征,提出了孔隙类球形、孔径分布连续的结论,并建立了孔隙孔径分布函数,推导了其概率密度函数。结果表明,变分图像分割方法作为孔隙提取的手段具有适用性和优越性,所提孔隙结构相关定量结果与试验数据具有较高的吻合度,基于此开展动态结冰微观结构定量研究是可行的。     

SiO_2-C复合气凝胶的制备及其结构

以间苯二酚(R)和甲醛(F)为碳源,以3-胺丙基三乙氧基硅烷(APTES)为硅源,一步溶胶一凝胶法简单快捷地合成了SiO_2-RF复合气凝胶,高温碳化后得到SiO_2-C复合气凝胶,并用扫描电镜、比表面分析仪对所得样品的结构进行了研究,并讨论了不同投料比对气凝胶结构的影响.结果表明碳化前,投料比APTES/R=1时,所得气凝胶具有最大的比表面积(S_(BET)=606.1 m~2/g),碳化后,由于体积收缩和酚醛热解产生新孔隙双重因素的影响,投料比AFTES/R=1/2时样品的比表面积达到最大(S_(BET)=704.2 m~2/g).     

多孔介质表面预混火焰熄火特性实验

对微型燃烧室中多孔介质表面预混火焰开展了不同孔径、孔隙率的多孔介质出口流场特性和熄火特性实验研究.研究结果表明:相对于圆管流,多孔介质出口流场边界层变薄,主流区宽度增加约50%,速度波动最大可达到前者的2.2倍.多孔介质孔径相同时,随孔隙率减小,或孔隙率相同时,随孔径减小,主流区的速度波动幅值均减小,在小孔径下更为明显,最大速度波动幅值从2.435m/s减小至1.099m/s.多孔介质表面预混火焰的熄火特性受出口流场和火焰形态的影响很大,孔隙率减小或孔径减小都会使相同当量比下熄火速度增加,多孔介质参数的影响最大可使熄火速度增加近1倍.