低温微量润滑技术喷嘴方位正交试验研究

低温微量润滑切削技术作为一种理想的绿色冷却润滑方式,已经成为机械加工领域研究的热点之一.选择外部微量润滑与低温冷风的集成作为低温微量润滑系统的实现方式,给出了确定系统喷嘴方位的3个参数:喷射方向与进给方向夹角β、喷嘴仰角α和喷嘴距切削区的距离d,并分别构建了其几何模型.针对β角,给出了最优β角与切宽半径比(B/R)的曲线.通过正交试验研究了喷嘴方位的3个参数(β、α、d)对低温微量润滑切削性能影响的重要程度.结果表明,距离d对切削性能的影响最大;其次是β角;α角的影响最小,可根据实际工况选择α在30°～60°即可.     

星图匹配制导中的关键技术

为了提高新一代弹道导弹的快速、机动反击能力和射击精度，采用星光，惯性组合制导足最佳的选择。本论文给出了基于双星敏感器的、星图匹配制导系统的关键技术。提出了根据弹道设计导航星表．极大地简化了弹载星表；提出了一种适用于星光制导的凸多边形箅法，合理地减少了匹配的星对角距数目。这两项技术保证了星图匹配制导技术的实用性。提出了一种分离初始定位、定向误差及平台漂移误差方法。采用凸多边形的星图识别算法可同时获得多颗星的瞬时位置，结合恒星在像平面的位置可解算导弹在赤道惯性系和发射点惯性系的三轴姿态，最后，给出了导弹初始定位、定向误差的数学表达式。仿真结果表明了该方法的有效性。     

Keeping Ma’at: An astronomical approach to the orientation of the temples in ancient Egypt

For various reasons, Archaeoastronomy has not been one of the favourite disciplines of the Egyptologists in the past. Probably because of that, important questions such as the orientation of Egyptian temples and the relevance of astronomy in this respect had never been afforded with the necessary seriousness and deepness. The Egyptian–Spanish Mission for the Archaeoastronomy of ancient Egypt has, among its various priorities, the solution of this problem. In order to achieve that, we have measured the orientation of some 330 temples in the Valley, the Delta, the Oases and the Sinai so far. The aim is to find a correct and almost definitive answer to the question of whether the ancient Egyptian sacred constructions were astronomically aligned or not. Our data seem to answer this question in the affirmative sense. Besides, they offer a very interesting new perspective in the field of landscape archaeology, a new discipline hardly worked in Egypt so far, in which terrestrial landscape, dominated by the Nile, and celestial landscape, dominated by the sun and the stars, would combine in order to permit the establishment of Ma’at, the Cosmic Order, on Earth.     

Microstructure,thermophysical property and ablation behavior of high thermal conductivity carbon/carbon composites after heat-treatment

Uni-directional carbon/carbon composites with high thermal conductivity are suitable to supply continuous thermal protection for future reentry vehicles since they could reduce surface temperature and ablation rates simultaneously in harsh environments. In this work, the high thermal conductivity carbon/carbon composites were prepared by chemical vapor infiltration. After heat-treatment, both their open porosity and internal friction increase due to the fiber/matrix thermal expansion mismatch; while their thermal conductive performance become better due to more complete carbon structure. With raising heat-treatment temperature from 1800 °C to 2450 °C, the mass and linear ablation rates of C/C composites with fibers vertical to the oxyacetylene torch for 60 s decrease from 0.66 mg/s and 2.95 μm/s to 0.51 mg/s and 2.05 μm/s respectively. The improved ablation resistance is resulted from the increased thermal conductivity from 282 to 508 W/(m·K) and more carbon fibers exposed to the flame during ablation, which have better oxidation resistance than those of carbon matrix. While such ablation rates become larger for composites with fibers parallel to the flame, from 1.02 mg/s and 3.73 μm/s to 1.28 mg/s and 5.01 μm/s respectively since the ablation occurred more easily through gaps at the fiber/matrix interfaces, which become larger and are always exposed to the flame for this case.     

Crystal orientation and morphology of α lamellae in wrought titanium alloys: On the role of microstructure evolution in β processing

To obtain high-quality aviation forgings of titanium alloys, β forging is an essential processing step which must be considered throughout a production process. In this work, the effect of β forging on the crystal orientation and morphology of lamellar α was experimentally investigated in a two-phase titanium alloy. Strong dynamic recovery during β working resulted in the formation of low-angle grain boundary (LAGB_β) inside β grains. The lamellar α can penetrate through the LAGB_β, leading to similar intra α LAGBs on subgrain boundaries. Deformation banding occurs at high strain rates, and both diffusive and sharp boundaries of deformation bands can be observed. A continuous change of the β orientation in diffusive boundaries results in the formation of fine and disordered α lamellae without intra-lamellar boundary to hold the Burgers orientation relationship (OR). On sharp boundaries, it is prone to producing continuous grain boundary α (α_GB) with a highly similar orientation along the boundaries. Meanwhile, there may exist several lower-angle boundaries within the grain boundary α for a smoother orientation change on the β grain boundary.     

Localization,Exploration, and Navigation Based on Qualitative Angle Information

Abstract

Three of the major problems in building autonomous mobile robots are localization, exploration, and navigation. This paper investigates how well different qualitative methods based on angle information, most of them originally invented for representation of spatial knowledge, are suited for addressing these problems. It combines results from discrete and computational geometry with methods from qualitative spatial reasoning, gaining some new insights on the complexity of robot navigation. It turns out that essentially only with panoramas (special roundviews) the qualitative localization problem can be solved in a satisfactory manner. The exploration problem (qualitative map building), remains difficult for all considered approaches.     

高温下取向对DD6单晶高温合金低周疲劳寿命的影响

对 76 0℃和 980℃两种温度下 [0 0 1],[0 11]和 [111]三种取向的DD6单晶高温合金的低周疲劳寿命进行了实验研究。结果表明 ,取向对其低周疲劳寿命有重要影响 ,[0 0 1]取向的寿命最高 ,[111]取向的寿命最低 ,通过引入应力幅值 ,可以在很大程度上消除取向的影响     

镍基单晶DD3涡轮叶片蠕变寿命晶向相关性分析

基于三维正交各向异性弹性有限元分析和晶体滑移理论，分析了单品涡轮叶片在其工作状态下的应力状态和蠕变寿命与叶型积叠线方向的晶体取向偏角、随机取向的晶向角之间的关系。分析结果表明：叶型积叠线方向的晶体取向偏角和随机取向的品向角，对单晶叶片的应力状态和蠕变寿命具有较大的影响，但二者对叶片蠕变寿命的影响规律是不同的。充分利用品体取向偏角和品向角，在不增加叶片重量的前提下，有利于进一步发掘材料潜力。因此对单晶叶片的晶向进行优化设计，具有重要的工程应用价值。     

闭合等角转位法的测量精确度

闭合等角转位法广泛地应用于传感器旋转式圆度测量仪、工作台旋转式圆度测量仪或精密轴系的径向、轴向及其综合误差的测量。对闭合等角转位法的测量精确度做了详细的理论分析和实验验证,并提出了正确确定其采样点数的方法。     

变目标方位角导引法

研究一种用于近程弹道式地－地弹的导引法，它是借用空－空弹常值目标方位角导引法的概念，把它改变成按弹道设计需要而变化的目标方位角导引法，去攻击地面固定目标，它有减小气动阻力，提高命中相对精度的优点，称它为变目标方位角导引法。