纳秒激光脉冲宽度对2024铝合金损伤特性的影响

飞机激光除漆对2024铝合金蒙皮可能造成潜在的损伤,需探究激光参数变化对基体材料表面的作用规律,其中脉冲宽度对激光-材料作用与材料损伤特性具有重要影响。本文采用COMSOL Multiphysics软件模拟分析了不同脉冲宽度时激光作用铝合金表面的温升特性,并借鉴ISO 11254 1-on-1激光损伤阈值测试方法研究了脉冲宽度对铝合金损伤阈值的影响,进一步分析了不同脉冲宽度下的烧蚀凹坑微观形貌、直径与深度变化规律。结果表明：铝合金表面峰值温度随脉冲宽度增加而降低;脉冲宽度从150 ns增加到240和330 ns时,铝合金损伤阈值从9.96 J/cm²分别增加到11.24和12.66 J/cm²,当激光能量密度达到损伤阈值时,3μm厚氧化膜被完全损伤,破坏了铝合金表面完整性;烧蚀凹坑直径和深度随脉冲宽度增加而增加,深度受影响程度更大。该研究可为激光与材料作用的脉冲宽度选择提供一定的参考。     

Investigation on induction brazing of profiled cBN wheel for grinding of Ti-6Al-4V

Profiled monolayer cBN wheel was induction brazed for grinding of titanium dovetail slot in this study. Aimed at acquiring a uniform temperature distribution along the profiled surface and reducing the thermal deformation of the brazed wheel, a finite element model was established to investigate the temperature uniformity during induction brazing. A suitable induction coil and the related working parameters were designed and chosen based on the simulation results. Ag-Cu-Ti alloy and cBN grains were applied in the induction brazing experiment. The results showed geometric deformation of the brazed wheel was no more than 0.01 mm and chemical reaction layer were found on the brazed joint interface. Further validation tests were carried out by grinding of Ti-6Al-4V alloy. Compared to the electroplated wheel, the brazed wheel showed better performance such as low specific grinding energy and good ground quality in grinding of Ti-6Al-4V alloy. Abrasion wear was found to be the main failure mode for the induction brazed wheel, while adhesion and grains pull-out were the main failure mode for the electroplated wheel.     

霍尔磁强计温度特性校准装置的研究

本文从霍尔元件的基本物理性能出发分析霍尔磁强计的哪些参数与温度有关，确定温度系数和零点温漂是影响霍尔磁强计特定温度下准确度的关键性参数，根据其工作原理开展了校准装置和校准方法的研究，本文阐述了这两套装置的工作原理和组成，并通过试验验证装置的测量能力。     

Multi-year behaviour of the midnight OH1 temperature according to observations at Zvenigorod over 2000–2016

Using spectral measurements of the hydroxyl airglow at the Zvenigorod station (56° N, 37° E), Moscow region, over 2000–2016, we obtained the long-term set of data comprising 1822 midnight values of the OH¹ temperature in the mesopause region. These data revealed a 17-year series of its mean annual values, as well as amplitudes and phases of the first two harmonics of its annual variation. The obtained parameters were analyzed to determine statistically relevant characteristics of their long-term variations. As a result, we found that the long-term behaviour of the mean annual OH¹ temperature features a small negative linear trend (?0.07 ± 0.03 K/year) over the addressed period. Besides, its dependence on solar activity is shown to be 4.1 ± 0.5 K/100 SFU. Regarding the long-term behaviour of the mean annual OH¹ temperature, we revealed the existence of two oscillations with 3-year (the amplitude being 1.3 ± 0.2 K) and 4.1-year (the amplitude being 0.6 ± 0.2 K) periods. We obtained empirical relations describing year-to-year variations in the amplitudes and phases of the annual and semi-annual harmonics.     

光纤法布里-珀罗传感器及其高温应用

随着航天技术不断发展，大推力运载火箭等精细化设计需求日益增加，飞行器高温工况结构及流场状态感知已成为当前研究的关键环节。基于法布里-珀罗干涉结构的光纤传感器在高温、高压、狭小空间等特殊环境展现出独特优势，被视为下一代高温原位测量工具。介绍了法布里-珀罗传感器的基本结构及原理，并分别从温度、应变和压力监测方面介绍了法布里-珀罗高温传感技术研究进展以及未来的发展趋势。基于石英光纤的法布里-珀罗传感器能够应用于1000°C以下环境，对于1000°C以上环境，需要以蓝宝石光纤作为敏感元件和传光介质。     

固体火箭复合结构喷管传热的隐式计算方法

采用适用于多层复合结构的当量热容瞬态热传导方程,通过坐标变换解决多个移动边界问题,用ADI方法推导了二维隐式求解格式,在与烧蚀相耦合的情况下获得了复合结构喷管的温度分布。用隐式方法计算有效地减少了计算机时,对工程设计大有裨益。     

First observation of upper mesospheric semi annual oscillations using ground based airglow measurements from Indian low latitudes

We summarize two years of Mesosphere Lower Thermosphere Photometer (MLTP) operation of mesospheric OH and O₂ emission monitoring. The deduced mesospheric OH and O₂ temperatures show large variability. Nightly temperature variations over Gadanki (13.5°N, 79.2°E) are dominated by the short period wave features, while tidal amplitudes are relatively small. Our measurements are the first to report a long period seasonal variation at two upper mesospheric altitudes simultaneously over the Indian sector. Our observations reveal the presence of a dominant semi-annual oscillation (∼6 months periodicity) together with a shorter period (∼2.5  months periodicity) oscillation in both OH and O₂ data.     

民用飞机空气导管内外温度分布研究

对空气导管内外温度分布进行了研究,建立具体的换热模型并采用两种方法进行了计算,同时还分析了导管布置对空气传热和流动特性的影响。     

前放组件高低温测试系统设计

对前放组件高低温测试系统设计开发的背景及意义作了简单介绍,并阐述了系统的组成结构及测量原理;详细地论述了测试系统中标准设备的选取、专用设备和夹具的设计思路,最后对测试系统的接地和屏蔽进行了概括总结。     

温控用电动百叶窗控制线路的设计

通过在某新型卫星立项攻关上的设计实例，介绍了一种设计方法；通过８０Ｃ３１单片机系统对有效载荷的温度变化进行及时采集监测，并根据卫星运行规律和温度控制要求对百叶窗进行及时有效的控制，在线路设计上采用了双ＣＰＵ系统控制和备份通道控制三套备份设计，极大地提高了控制线路工作的可靠性，能满足卫星工作的要求。