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.     

一种实现飞行品质参数实时辨识的实用方法

考虑到辨识算法收敛的可靠性及结果的精度，采用递推最小二乘估计、飞机运动模态连续－离散模型相互转换及递推极大似然估计，实现飞行品质参数的实时辨识。这种方法的优点在于算法的吸收域是全平面的。初值不影响算法的收敛性，能很好地满足实时性要求，同时还保证了结果精度。利用该方法对某型飞机铁鸟台实测数据进行了处理，取得了满意的结果。     

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。     

数字仿真在航空可靠性工程中的应用

回顾近10年来蒙特卡罗数字仿真在我国航空可靠性工程领域的应用和发展,它展示出可靠性仿真在该领域的作用和地位。最后,对今后可靠性仿真研究提出了几点看法。     

多传感器信息融合技术在现代战机设计中的应用

基于综合航电系统设计中的关键技术———信息融合 ,介绍了信息融合的概念、目标跟踪的算法及传感器的管理 ,以此说明现代作战飞机应用信息融合技术可增强作战平台在恶劣战场环境下的生存能力