焊接方式对铝合金搅拌摩擦焊T 型接头性能的影响

采用4种规格的搅拌头进行了2A70-T6铝合金T型接头搅拌摩擦焊试验,并对焊缝横截面进行了观察以及焊缝抗拉强度的测试.结果表明:焊缝中前进侧熔合过渡区的金属变形比返回侧剧烈,焊缝断裂往往发生在前进侧;在相同的焊接参数下,单道焊缝的焊核宽度与抗拉强度随着搅拌针直径的增大而增大,但增大的幅度较小,并列焊的焊缝抗拉强度仅为单道焊缝的93％左右;为了获取相同宽度的焊核,采用加粗搅拌针单道焊比并列焊更具有优势.     

高温空气电子浓度的实验测定及对理论图表的检验

本文总结了近几年来在φ800mm激波管上对高温空气电子密度所做的大量测量工作。在ρ_1=1.3—133帕斯卡,M_s=9—22.5的范围内,使用了近自由分子流Langmuir探针、普通微波透射仪、高灵敏度微波透射仪和反射仪、微波干涉仪等对正激波后的电子密度进行了系统地测量。在各种参数状态下,全部实验数据均符合在同一激波马赫数下n_g正比于ρ_1的经验规律。实验测量结果与目前工程上常用的各种理论计算图表进行了对比,验证了这些图表的可用性。     

异性材料对接和搭接焊的高温性能对比试验研究

通过对K163-GH3030材料对接和搭接焊进行高温瞬时拉伸、高温疲劳寿命试验，得出该对接和搭接焊接头的S—N曲线，举例评定了构件的疲劳寿命，比较分析了对接焊与搭接焊疲劳寿命的差异。指出了在承力结构中应该尽量避免搭接焊。     

GEM-TEPC调研分析及原理研究

为对现有组织等效正比计数器进行改进,使其满足高注量率辐射场测量要求,本实验室拟研制一套基于气体电子倍增技术的宽量程TEPC。对GEM-TEPC工作原理进行研究,并对其国际发展现状进行调研,在传统的TEPC灵敏体积内引入GEM膜取代阳极丝是切实可行的,可降低微型TEPC探测器的加工难度,提高其性能。通过调研总结GEM-TEPC设计关键技术,为本实验室GEM-TEPC的研制奠定了一定基础。     

Effects of different aging treatments on microstructures and mechanical properties of Al-Cu-Li alloy joints welded by electron beam welding

Post-weld single aging treatment(solution treatment at 510 ℃ for 1 h, water quenching,and aging at 155 ℃ for 16 h) and post-weld double aging treatment(solution treatment at 510 ℃ for 1 h, water quenching, aging at 155 ℃ for 16 h, and aging at 130 ℃ for 12 h) are carried out on Al-Cu-Li alloy joints by electron beam welding(EBW) respectively. The effects of aging treatments on microstructures and mechanical properties of welded joints are investigated. Results show that the mechanical properties of welded joints are obviously improved after both aging treatments. The strength coefficient of joints is increased from 0.64 in an as-welded condition(AW) to 0.90 after post-weld double aging treatment. Microstructure analysis shows that the precipitates of the fusion zone within grains and grain boundaries are less in the AW condition. After post-weld heat treatment(PWHT), a lot of fine needle-like phases T_1(Al_2 Cu Li) precipitate in grain boundaries of the fusion zone, and more horseshoe-shaped β' (Al_3 Zr) particles precipitate within grains. In addition,grains of the fusion zone are refined after post-weld double aging treatment, which leads to an effect of grain refinement strengthening. Consequently, the mechanical properties of welded joints are greatly improved.     

Studies of electron and ion temperatures at 500 km altitude during sunrise using Indian SROSS C2 satellite

Solar dependence of electron and ion temperatures (T_e and T_i) in the ionosphere is studied using RPA data onboard SROSS C2 at an altitude of ∼500 km and 77°E longitude during early morning hours (04:00–07:00 LT) for three solar activities: solar minimum, moderate and maximum during winter, summer and equinox months in 10°S–20°N geomagnetic latitude. In winter the morning overshoot phenomenon is observed around 06:00 LT (T_e enhances to ∼4000 K) during low-solar activity and to T_e ∼ 3800 K, during higher solar activity. In summer, it is observed around 05:30 LT, but the rate of T_e enhancement is higher during moderate solar activity (∼2700 K/hr) than the low-solar activity (∼1700 K/hr). During equinox, this phenomenon is delayed and is observed around 06:00 LT (∼4200 K) during all three activities.     

Wave emissions at half electron gyroharmonics in the equatorial plasmasphere region: CLUSTER observations and statistics

Intense (n + 1/2) f_ce emissions are a common phenomenon observed in the terrestrial inner magnetosphere. One of their interests is their possible effect in the pitch angle scattering of plasmasheet keV-electron, leading to diffuse auroras. In this paper, we present CLUSTER’s point of view about this topic, in the equatorial region of the plasmasphere, via a statistical study using 3 years of data. Spectral characteristics of these waves, which represent an important clue concerning their generation mechanism, are obtained using WHISPER data near perigee. Details on the wave spectral signature are shown in an event study, in particular their splitting in fine frequency bands. The orbit configuration of the four spacecraft offers a complete sampling on all MLT sectors. A higher occurrence rate of the emissions in the dawn sector and their confinement to the geomagnetic equator, pointed out in previous studies, are confirmed and described with additional details. The proximity of emission sites, both to the plasmapause layer and to the geomagnetic equator surface, seems to be of great importance in the behaviour of the (n + 1/2) f_ce wave characteristics. Our study indicates for the first time, that both the intensity of (n + 1/2) f_ce emissions, and the number of harmonic bands they cover, are increasing as the observation point is located further away outside from the plasmapause layer. Moreover, a study of the wave intensity in the first harmonic band (near 3/2 f_ce) shows higher amplitude for these emissions than previous published values, these emissions can play a role in the scattering of hot electrons. Finally, geomagnetic activity influence, studied via time series of the D_st index preceding observations, indicates that (n + 1/2) f_ce emission events are observed at CLUSTER position under moderate geomagnetic activity conditions, no specific D_st time variation being required.     

行星际磁云边界层中的电子分布函数特征

基于WIND 飞船观测的1995---2006 年间的磁云事件, 研究了磁云边界层中电子的流动图样, 以及电子速度分布函数的特点与电子加热和加速的关系, 得出以下结果. ①磁云边界层中存在的电子流动图样, 包括各向同性、双向流动和单向流动等. ② 相比于背景太阳风和磁云本体, 通常情况下磁云边界层中电子分布函数的核心热电子成分 (E<60eV) 增多, 超热电子成分 (E>60eV) 在沿磁场垂直方向上增多, 而在沿磁场平行或反平行方向以单方向增加为主, 此外, 还在近1/10 的磁云边界层中观测到了高能电子的明显增多. ③对比研究了磁云边界层与磁云驱动的激波对电子速度分布函数的调制作用, 经过激波, 电子分布函数的超热电子成分在各方向上都有增加, 不同于磁云边界层中在沿磁场平行或反平行方向上超热电子成分以单方向增加为主, 表明二者有不同的形成机制. ④考察了磁云边界层中的波活动增强和电子分布函数及离子流量增加的对应关系. 上述观测和对比分析进一步表明了磁云边界层是一种重要的动力学结构, 磁重联是一种可能的形成机制.     

三向碳-碳复合材料界面结构研究

本文用透射电子显微术研究了三向碳-碳复合材料的界面结构。结果表明:在碳纤维表面微缺陷区或活性区,存在沉积碳微晶条带“钉扎”结构;在碳纤维表面光滑区,存在一定数量的界面间隙:沥青碳与沉积碳的界面存在一个沉积碳微晶条带与沥青碳石墨条带相互贯穿网络所形成的诱导结构界面相。本文分析了界面缺陷,并讨论了界面结构对纤维束断裂行为的影响。     

自锁阀激光焊接工艺研究

研究了自锁阀激光焊接焦点位置与焊缝熔深之间的关系、焊接速度和激光功率与焊缝熔深之间的关系,分析了随着激光功率增加,不同焦点位置的焊接过程依次经历稳定热导焊,热导焊、深熔焊交替进行的不稳定焊接和稳定深熔焊接三种模式,进而研究了稳定焊接模式下工艺参数与焊缝熔深之间的关系,得出了自锁阀在稳定焊接模式下的最佳焊接工艺规范参数.采用该激光焊接工艺规范焊接的常压和高压自锁阀焊缝外观质量、气密、液压以及焊缝氦质谱检漏试验结果全部满足设计要求.常压和高压自锁阀已经应用于嫦娥五号、探月工程、东风导弹武器系统、货运飞船、921-3推进分系统、东方红三号等推进系统的液体火箭发动机之中.