TC4钛合金腐蚀加工速度和表面质量影响因素研究

研究了腐蚀溶液成分和工艺参数对TC4钛合金腐蚀加工速度、表面粗糙度和平整度的影响,利用扫描电镜观察了腐蚀加工前后的表面形貌.研究结果表明:氢氟酸浓度和溶液温度直接决定着腐蚀加工速度,随HF浓度和温度的增加,腐蚀加工速度升高.硝酸具有显著降低表面粗糙度的作用.溶液中的钛离子对腐蚀加工速度以及钛合金零件腐蚀后的表面质量有一定的影响,溶液中钛离子含量较低时,腐蚀加工速度较快,表面平整度较好,随钛离子含量的增加,腐蚀加工速度下降,表面不平整度增加.试样垂直吊挂时,定时翻转并搅拌可以得到均匀腐蚀的表面.     

Equivalent model of close-packed film cooling holes in nickel-based single crystal cooled blade based on crystallographic theory

The mechanical properties of nickel-based single crystal thin-walled plate with close-packed film cooling holes were studied based on the equivalent solid material concept. The effective plastic parameters inversion method based on crystallographic theory were proposed. A simplification method for close-packed film cooling hole plates with square and triangular penetration patterns was presented. A large number of finite element analysis results covering different ligament efficiencies and penetration patterns were provided to verify the feasibility of the plastic equivalent principle and simplification method. The results show that the stress–strain curve and resolved shear stresses of simplification models are in consistence with the plate models with close-packed film cooling holes. The equivalent errors of yield strength are all within the error band and the values of equivalent errors are all less than 10%. In addition, the equivalent errors of the positions where maximum resolved shear stress occurs are all less than 15°, indicating the accuracy of plastic equivalent model and simplification method.     

CO2用于气动弹射的可行性分析

针对传统气动弹射介质空气做功能力不足的问题,提出采用CO_2作为新型气动弹射介质。基于质量守恒和能量守恒定律建立了以CO_2为弹射介质的弹射热力模型,并使用该模型对比分析了CO_2和空气作为弹射介质对于弹射性能的影响。得到了弹射过程中高低压室内介质状态以及飞行器运动参数的动态变化过程。与空气相比,CO_2具有更大的做功能力。相同的热力状态下弹射相同质量的飞行器,使用CO_2可获得更大的出筒速度。CO_2作为弹射工质对于大质量的飞行器优势明显,在不减小出筒速度的情况下,使用CO_2可使负载质量提升50%以上,验证了CO_2作为弹射工质的可行性。     

A wall-thickness compensation strategy for wax pattern of hollow turbine blade

As an important index affecting the aerodynamic performance and the structural strength of hollow turbine blades, the wall-thickness precision of the blade is mainly inherited from the positional relationship between the corresponding wax pattern and the internal ceramic core. However, due to locating errors, the actual position of ceramic core is always deviated from the ideal position, which makes it difficult to guarantee the wall-thickness precision of the wax pattern. To solve this problem, a wall-thickness compensation strategy is proposed in this paper. Firstly, based on the industrial computed tomography (ICT) technique and curve matching algorithms, a model reconstruction method is developed, with which the 3D model of a trial wax pattern can be easily constructed. After that, focusing on eliminating the wall-thickness errors of the trial wax pattern, an optimization method for the pose of the ceramic core in the wax pattern is proposed. Then, by mapping the optimal pose of the ceramic core to length adjustments of the locating rods, the wall-thickness errors of the wax pattern can be greatly reduced. A case study is also given to illustrate the effectiveness of the proposed compensation strategy.     

EXPERIMENTAL STUDY OF TURBULENT WINGBODY JUNCTION AND WAKE FLOW

ＥＸＰＥＲＩＭＥＮＴＡＬ　ＳＴＵＤＹ　ＯＦ　ＴＵＲＢＵＬＥＮＴ　ＷＩＮＧＢＯＤＹ　ＪＵＮＣＴＩＯＮ　ＡＮＤ　ＷＡＫＥＦＬＯＷＫａｎｇＨｏｎｇｗｅｎ；ＦａｎＭｅｎｇ；ＷｅｉＺｈｏｎｇｌｅｉ（ＤｅｐａｒｔｍｅｎｔｏｆＭｅｃｈａｎｉｃｓ，ＰｅｋｉｎｇＵｎｉ...     

用自联想网络处理带噪声的发动机数据

研究了用自联想网络(AANN)进行数字滤波的方法。自联想网络采用一种带有瓶颈层的特殊结构，且具有单位总增益。在经过大量带噪声样本的训练之后，各变量之间能够建立起内在联系。输入信息通过瓶颈层前的压缩及瓶颈层后的解压缩过程，信息中的精华将被提取，从而使人们能够利用冗余信息抑制其测量噪声，使发动机测量参数在最大程度上减少噪声对其带来的负面影响。     

关于有理Bézier曲面片的几何连续拼接问题

本文深入研究了有理Bézier曲面片的几何连续拼接问题,给出了GC~1拼接条件的显式表示和判断两曲面片GC~1拼接状况的判定条件。用此条件可编写一简单程序,通过输入两曲面片的控制顶点及权因子,便可以“YES”或“NO”的输出回答两曲面片的拼接是否为GC~1连续。在非GC~1拼接时,可对称地修改两曲面片使其GC~1拼接。最后,本文给出了几种CAD/CAM工程中实用的充分条件。     

压杆稳定可靠性稳健设计

将稳定可靠性优化理论、稳定可靠性灵敏度技术与稳健设计方法相结合,讨论压杆稳定可靠性稳健设计问题,提出了稳定可靠性稳健设计的计算方法。把可靠性灵敏度溶入可靠性优化设计模型之中,将可靠性稳健设计归结为满足可靠性要求的多目标优化问题。数值算例表明所提数值计算方法是一种非常方便和实用的可靠性稳健设计方法。     

某型飞机空中飘摆故障分析及防护措施

分析某型飞机平尾助力器故障导致飞机在空中飞行时产生飘摆现象的原因,提出修理改进措施及维护对策。     

航空复合材料纸蜂窝夹芯结构热成型开裂研究

飞机复合材料芳纶纸蜂窝夹芯部件在热压罐成型时处于热-力耦合工况。本文关注热成型过程中可能出现的蜂窝开裂现象,通过试验获得了蜂窝芯的拉、压、剪性能参数和芳纶纸的热性能参数,同时结合有限元分析手段和反演方法,对整体蜂窝夹芯部件的热-力顺序耦合和局部芯子抽真空导致的蜂窝胞元间压强差进行数值模拟。结果表明：成型过程中的热应力不会导致蜂窝胞元间胶层开裂,局部憋气的压差可能导致蜂窝开裂;胶层部分破坏与胶层完全破坏所需的胞元间压强差的差值与胶层初始法向断裂应力正相关;胶层完全破坏所需的胞元间压强差随着受载胞元数量的增多而减小。