无人机软着陆气囊缓冲特性研究

以上单翼布局无人机为对象,建立软着陆气囊缓冲系统的简化解析模型,开展了气囊软着陆系统缓冲特性的研究。在此基础上,进一步确定气囊设计参数的可行取值域,选取气囊初始设计参数。之后,构建缓冲系统的动力学有限元模型,分析了气囊设计参数及着陆姿态对于缓冲效果的影响。研究结果表明,正常着陆工况下,解析模型得到的气囊设计参数对无人机质心过载峰值的影响规律与有限元分析结果基本一致,不过由于解析模型中引入了多个假设,两种方法得到的过载峰值大小存在差异。当着陆存在初始姿态角时,会加重无人机缓冲过程中的俯仰与滚转运动,易造成机体的损坏。为了避免二次硬冲击带来的局部意外损害,提出一种组合型气囊设计方案。仿真分析表明,应用组合型气囊可以在缓冲后段提供有效的软支撑作用,避免无人机发生二次硬冲击和反弹翻覆。     

航空发动机涡轮叶片裂纹检测信号特征提取

航空发动机涡轮叶片是高精密重要器件,其表面微裂纹检测属于不规则曲面检测的一种,是无损检测领域研究的热点和难点。考虑到涡流检测的特有优势,设计了一种不同于传统方式的简单实用且有效的差激励涡流探头,实现对涡轮叶片预制微裂纹的识别。由于叶片表面为曲率变化的弧面,检测过程难免会发生提离,因此获得的检测信号中包含噪声和多个奇异点等多种干扰因素。为保证缺陷位置重要信息不丢失,采用镜像延拓经验模态分解（EMD）重构与小波奇异性检测相结合的方法对得到的微裂纹信号进行处理,滤除了非裂纹位置的多处畸变点影响,有效准确地实现了叶片微裂纹位置的判定。实验结果表明,该方法可以有效降低检测信号的噪声和干扰,准确提取裂纹信号特征信息,对飞机涡轮叶片类零件微缺陷的早期检测和完整有效性评估具有一定的借鉴意义。     

Experimental investigation on thermo‐driving heat transfer in porous medium in a centrifugal force field

Based on the research in turbine blade super cooling techniques, experiments were carried out to investigate the thermo‐driving heat transfer phenomenon in a new cooling configuration filled with porous medium in a centrifugal force field. Moreover, the heat transfer effectiveness of the configuration was compared to one with no porous medium. The results showed that the thermo‐driving heat transfer effectiveness of the configuration filled with porous medium could be enhanced by increasing the rotating speed, heat flux, and cooling air speed. Meanwhile, the heat transfer effectiveness of the configuration was strengthened with the installation of porous medium. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(6): 329– 338, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20219     

NICKEL-BASE ALLOY SHEET ALLOYS USED IN AEROSPACE APPLICATIONS

ＮＩＣＫＥＬ－ＢＡＳＥＡＬＬＯＹＳＨＥＥＴＡＬＬＯＹＳＵＳＥＤＩＮＡＥＲＯＳＰＡＣＥＡＰＰＬＩＣＡＴＩＯＮＳＪ．Ｈ．Ｔｕｎｄｅｒｍａｎｎ（ＩｎｃｏＡｌｌｏｙｓＩｎｔｅｒｎａｔｉｏｎａｌ,Ｉｎｃ．,Ｈｕｎｔｉｎｇｔｏｎ,ＷＶ２５７０５,ＵＳＡＭａｎｕｓ...     

预腐蚀7050-T7651铝合金微裂纹的萌生与扩展北大核心

开展不同预腐蚀时间下7050-T7651铝合金的扫描电子显微镜原位拉伸实验,利用扫描电子显微镜观原位、在线测试件表面微观裂纹的萌生、扩展,分析腐蚀对铝合金微裂纹行为的影响。结果表明:随着腐蚀程度加剧,试件表面腐蚀坑密度增大,形成腐蚀坑群,试件的承载能力也随之下降。微裂纹主要萌生于试件缺口粗糙表面和试件表面蚀坑处,微裂纹数量随着腐蚀时间的延长而增多;缺口产生的微裂纹与相邻的蚀坑微裂纹相互联结形成主裂纹,主导试件的损伤失效过程。腐蚀损伤较轻时,主裂纹尖端附近的蚀坑会引起裂纹分支;腐蚀损伤较重时,腐蚀坑诱导的多条微裂纹与主裂纹发生多次联合,影响了主裂纹的扩展方向与路径;切应力在裂纹扩展过程中也起到了重要作用,开裂模式为Ⅰ/Ⅱ混合断裂模式。     

Greening Industrially Applied Toxic Cadmium Plating with γ-Ni2Zn11 Alloy in Deep Eutectic Solvents: Promising Electroplating Efficiency and Chemical Corrosion Resistance

Cadmium is an industrially applied plating metal used in aerospace applications, but electrodeposition of cadmium is toxic, and current production method will soon be banned. Therefore, electrodeposition of alternative alloys in environmentally friendly solutions is an attractive research area. An additive-free, nonaqueous, deep eutectic solvent (DES) containing Ni and Zn halide salts is developed in a greener environmental method. Gamma-phase nanocrystalline Ni₂Zn₁₁ is coated onto hot-rolled mild steel via pulse reverse current (PRC) in the developed nonaqueous solvent. The employed DES’ relatively low viscosity and sufficient conductivity enable the simultaneous reduction of Ni²⁺ and Zn²⁺ cations on microelectrode. Electrochemical quartz crystal microbalance (eQCM) analysis proves the absence of the commonly reported problem of electrode blocking during electrodeposition, revealing an efficiency of 86.07%. Appropriate PRC parameters are applied for scaled macroelectrode deposition. The plating profile exhibits 20 μm-thick alloy deposition without cracks around 3 h. Scanning electron microscopy–electron-dispersive spectroscopy and X-ray diffraction analyses reveal that 15.5 wt% Ni is in the nanograin phase, and all crystal planes belong to the γ-Ni₂Zn₁₁ phase, which is needed as an alternative to cadmium plating. Hardness and corrosion tests performed on the γ-Ni₂Zn₁₁ coating reveal better hardness and corrosion resistance with supporting morphological evidence.     

Comparative assessment of force,temperature, and wheel wear in sustainable grinding aerospace alloy using biolubricant

The substitution of biolubricant for mineral cutting fluids in aerospace material grinding is an inevitable development direction, under the requirements of the worldwide carbon emission strategy. However, serious tool wear and workpiece damage in difficult-to-machine material grinding challenges the availability of using biolubricants via minimum quantity lubrication. The primary cause for this condition is the unknown and complex influencing mechanisms of the biolubricant physicochemical properties on grindability. In this review, a comparative assessment of grindability is performed using titanium alloy, nickel-based alloy, and high-strength steel. Firstly, this work considers the physicochemical properties as the main factors, and the antifriction and heat dissipation behaviours of biolubricant in a high temperature and pressure interface are comprehensively analysed. Secondly, the comparative assessment of force, temperature, wheel wear and workpiece surface for titanium alloy, nickel-based alloy, and high-strength steel confirms that biolubricant is a potential replacement of traditional cutting fluids because of its improved lubrication and cooling performance. High-viscosity biolubricant and nano-enhancers with high thermal conductivity are recommended for titanium alloy to solve the burn puzzle of the workpiece. Biolubricant with high viscosity and high fatty acid saturation characteristics should be used to overcome the bottleneck of wheel wear and nickel-based alloy surface burn. The nano-enhancers with high hardness and spherical characteristics are better choices. Furthermore, a different option is available for high-strength steel grinding, which needs low-viscosity biolubricant to address the debris breaking difficulty and wheel clogging. Finally, the current challenges and potential methods are proposed to promote the application of biolubricant.     

基于滤波网络的多余物状态识别研究

在航天产品的研发制造过程中,多余物控制至关重要,尤其是多余物状态识别的环节,其核心在于如何有效提取高噪声图像中的局部特征。现有方法尚未针对多余物场景进行有效建模,通用的视觉模型往往会对噪声进行过度拟合,而无法有效滤除噪声信号。为此,提出了一种可学习滤波感知机。该感知机通过采用一种可学习滤波器来替代繁琐的自注意力机制,用以学习空间位置的交互作用信息。随后,引入了频谱掩模用于频域分量特征的抽取,以学习不同频段内的重点信息。实验结果表明,该方法在多余物识别中取得了96.7%的准确率,优于基于卷积和自注意力的模型,并且具有更低的计算复杂度。     

Multi-Material Inconel 718 Parts with Highly Conductive Copper Cooling Channels for Aerospace Applications

Multi-material parts can offer valuable solutions to engineering problems when compared to single materials. The conceptualization of a multifunctional Inconel 718 (IN718)–Copper (Cu) solution aims to improve the heat extraction capacity of an aerospace component. High-strength IN718 was used as the base material and highly thermal conductive Cu was employed for internal cooling channels. The cooling channels are produced by electrical discharge machining (EDM) and subsequently filled with Cu to be sintered by hot pressing (HP). The morphological, microstructural, hardness, and thermal properties of the hot-pressed multi-material IN718–Cu specimens are studied to evaluate the feasibility of HP processing as a viable manufacturing approach for these multi-material solutions. The multi-material IN718–Cu specimens presents a well-defined design with good metallurgical bonding between the two materials and a thin diffusion region is found, assuring the final properties of each individual material. The Vickers’ microhardness of IN178 and Cu are in accordance with the reported for conventional processes which indicates good densification. The thermal conductivity of the multi-material IN718–Cu specimen is 25% higher than mono-material IN718, which can be a significant improvement in the thermal efficiency of an aerospace component.     

一种点火控制系统自动测试设备设计与应用

点火控制系统在地面测试阶段往往会进行多次重复性测试,以便及时掌握点火控制系统在经历不同试验后的性能状态情况,为了在保证测试精度和测试稳定性的同时提升测试效率,设计研制了一种点火控制系统自动测试设备,搭建出基于PXI总线的控制系统,实现对点火控制系统的供电控制、数据采集和性能验证等功能,以LabVIEW开发平台设计了对应的测试软件,经实际试验验证,所搭建的测试设备能够以较高稳定性和精确度实现对点火控制系统的功能性能测试。