颗粒尺寸对SiCP/Al复合材料疲劳裂纹扩展速率的影响

研究了轴向载荷下,对3种S iC粒子(5,20和60μm)增强的2024铝合金复合材料疲劳裂纹扩展速率及颗粒尺寸的影响。复合材料疲劳裂纹扩展速率随颗粒尺寸增加而减小。去除裂纹闭合影响后,3种复合材料间疲劳裂纹扩展速率差消除了,但是复合材料的裂纹扩展速率低于2024铝合金的。     

粉末粒度对快速凝固／粉末冶金Al-Fe-Mo-Si／Zn-Al复合材料组织与性能的影响

研究不同粉末粒度Al-9.0?-1.8%Mo-1.7%Si/5%(Zn-30%Al)金属/金属复合材料的组织、拉伸性能和阻尼性能.快速凝固粉末由气体雾化制备,选取平均粒度d50分别为27.3,36.2,41.6μm粉末装入包套,经除气,再热挤压制成棒材.结果表明,粉末粒径越粗,强化相越粗大,呈团聚体存在,且有偏聚现象,材料的强度明显下降,室温下粉末较细材料的阻尼性能较好,高于100℃时粉末粒度较粗材料的阻尼性能好.     

旋转封闭循环小通道内液态金属热驱动换热特性研究

高速旋转条件下,封闭循环小通道内的流体(热驱动介质)在浮升力的作用下会产生热驱动运动,将热量不断的从高温端携带至冷却端释放。本文通过数值模拟的方法,研究了离心力场下封闭循环小通道中,不同性质流体的流动和换热特性。重点分析了以液态金属锂、钠和钠钾合金为热驱动介质时,热驱动运动的换热特性Nu随Bu和Ro两个参数的变化规律。研究中发现在一定的Bu数变化范围内,以液态金属锂、钠以及钠钾合金为热驱动介质所得到的Nu均随Ro数的增大而减小;当Ro数相同时,Nu随Bu数的增加而变大。研究结果表明高转速,低加热量时,采用液态钠钾合金为热驱动介质可以得到最好的热驱动换热效果;在高转速,高加热量时以液态锂为热驱动介质时,热驱动换热能力最强。      

Location of Magnetic Reconnection in the Magnetotail

It is a crucial issue to know where magnetic reconnection takes place in the near-Earth magnetotail for substorm onsets. It is found on the basis of Geotail observations that the factor that controls the magnetic reconnection site in the magnetotail is the solar wind energy input. Magnetic reconnection forms close to (far from) the Earth in the magnetotail for high (low) solar wind energy input conditions.With the early Vela spacecraft observations, it was believed that magnetic reconnection started inside the Vela position, likely at 15 R_E. The later ISEE/IRM observations put magnetic reconnection beyond 20 R_E. The Vela event studies were made for highly active conditions, while the ISEE/IRM survey studies were made for moderate or quiet conditions. The finding of the factor that controls the site of magnetic reconnection in the magnetotail resolves the apparent discrepancy among various spacecraft results, and suggests solar cycle variation of the magnetotail reconnection site.     

Electron Beam-Physical Vapor Deposited TiAl-based Laminated Composite Sheet with Nb Layer Toughening

The TiAl-based laminated composite sheet of 150mm×100 mm×0.2mm, with 24 TiAl layers and 23 Nb layers laid alternately one on another, was successfully fabricated using the electron beam-physical vapor deposition (EB-PVD) method. The microstructure and properties of the sheet were investigated on an atomic force microscope (AFM), a scanning electron microscope (SEM) and a tensile testing machine. The results indicate that the evenly distributed Nb layers are well joined with the TiAl layers, and the interfaces between layers are transparent, and every interlayer spacing is of about 8 μm. The fractures appear to be a mixture of intergranular fractures and somewhat ductile quasi-cleavage ones. Despite its slight influence on ultimate tensile strength, the inserts of Nb layers efficiently in-crease the room temperature ductility of TiAl-based alloys due to the crack deflection effect.     

Preparation of SiC_p/Al_2O_3-Al Composites by Directed Metal Oxidation

SiCp/Al2O3-Al composites were synthesized by means of direct metal oxidation method. The composition and microstructures of the composites were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and metallurgical microscope. The effects of technical parameters on the properties of the product were analyzed. The results indicate that the composite possesses a dense microstructure, composed of three interpenetrated phases. Of them, SiO2 layer prohibits the powdering of the composites; Mg promotes the wetting and infiltration of the system and Si restricts the interfacial reaction while improving the wetting ability between reinforcement and matrix.     

基于Event的垂直碰撞风险改进模型研究

空中交通流量的快速增长,导致空域资源紧张和大量航班延误。使用新航行技术缩小间隔标准可以有效地缓解上述问题。因此,对航路的碰撞风险进行评估具有重要意义。传统Event模型的碰撞模板是一个长方体模板,本文在前人研究的基础上提出了用椭球体代替长方体碰撞模板的思想,并对飞机穿越垂直间隔片的概率重新进行计算。结果表明,在相同条件下改进后的Event碰撞风险模型是原模型碰撞概率的53.38%,改进的碰撞风险评估模型更加精确合理。     

盘轴件涡流扫查系统的研制

由计算机、涡流探伤仪、电机控制单元、4轴机械扫描器、放置式探头及其卡具组成扫查系统,可对盘轴件上平面、圆盘面、圆柱面、圆台面等部位进行自动扫查,相对于传统手动涡流检测,具有灵敏度高、结果直观、效率高等优点。本文介绍了系统的设计方法,分析了其中若干技术问题,并给出了部分实验结果。     

基于单叶双曲面的标准Stewart并联结构六维力传感器各向同性优化设计

基于Stewart并联结构六维力/力矩传感器在空间六维力的准确检测上具有广泛前景,设计低耦合、高精度、易于标定和使用的六维力/力矩传感器是其结构设计的关键问题.传统Stewart并联结构几何参数描述为6个相互耦合的变量,不利于实现设计参数与设计指标的解耦,而且非正交条件下的各向同性使得六维力/力矩传感器仍存在耦合,为此...     

TA2M钛板扩孔成形中的形状畸变现象研究

通过有限元数值模拟和工艺试验相结合的方法对板料厚度为0.96mm的TA2M钛板的扩孔成形过程及结果进行了研究.运用PAM-STAMP有限元数值模拟分析软件对成型过程及卸载回弹结果进行预测.发现TA2M在成型卸载回弹后存在明显的形状畸变现象:孔口非圆化,孔口边缘厚度非均匀减薄以及凸缘非圆化.模拟预测结果与工艺试验结果比较吻合.