钛合金表面缺陷的激光熔覆修复研究

采用激光熔覆方法对钛合金试样表面缺陷进行修复,对修复结果进行反复测试,并与氩弧焊修复进行对比试验。试验结果表明,激光熔覆可实现对钛合金表面缺陷的有效修复,且各方面性能远高于氩弧焊修复。     

含中央分层缺陷层合板的压缩性能研究

通过考察层合板厚度(含铺层形式)、分层位置与大小等因素对压缩强度的影响,并采用局部屈曲、分层扩展以及软化夹杂等3种模型对含分层层合板的压缩强度进行了计算和破坏机理分析。得出如下结果:厚板对分层缺陷不敏感,中等厚度和薄层合板比较敏感;缺陷的位置和大小对层合板压缩强度的影响没有明显的规律可循;3种模型中软化夹杂模型效果较好,说明大部分含缺陷层合板的压缩过程具有分层扩展、基体开裂等损伤交杂在一起的特点,这导致了试件的破坏。     

二维装药内弹道数值模拟改进方法

研究了长细比大的管形装药固体火箭发动机在燃烧过程中的侵蚀燃烧和滞点漂移现象，视燃烧产物为准定常流动，使用分段解析法，进行内流场的数据模拟，并对滞点漂移进行了计算。     

疲劳裂纹随机扩展模型

疲劳裂纺在扩展过程中有很大分散性，根据不同的来源将这种分散性归为两类：材料固有的内在分散和外、环境等引起的外在分散性。     

空空导弹弹体典型焊接缺陷及其控制技术

介绍了空空导弹弹体的结构特点、焊接技术要求、所用材料及常用的焊接方法,分析了圆周焊缝典型的焊接缺陷、危害及产生原因等,并就如何防止和消除焊接缺陷进行了深入的探讨,同时介绍了几种控制焊接缺陷的工艺方法。     

Variable stiffness design of redundantly actuated planar rotational parallel mechanisms

Redundantly actuated planar rotational parallel mechanisms (RAPRPMs) adapt to the requirements of robots under different working conditions by changing the antagonistic internal force to tune their stiffness. The geometrical parameters of the mechanism impact the performances of modulating stiffness. Analytical expressions relating stiffness and geometrical parameters of the mechanism were formulated to obtain the necessary conditions of variable stiffness. A novel method of variable stiffness design was presented to optimize the geometrical parameters of the mechanism. The stiffness variation with the internal force was maximized. The dynamic change of stiffness with the dynamic location of the mechanism was minimized, and the robustness of stiff-ness during the motion of the mechanism was ensured. This new approach to variable stiffness design can enable off-line planning of the internal force to avoid the difficulties of on-line control of the internal force.     

"流行书风"的内在特征与形成原因

"流行书风"的形成与当时书法艺术家主体的完全独立、书法理论界的思想解放、创作主体对创作的个性化与原创性追求,以及以国家级的展览为代表的展厅文化的推波助澜息惠相关.只要其"根植传统、张扬个性"的宗旨不变,在当前乃至今后一个较长的时期,它将一如既往地继续"流行".     

含天然与人工内部缺陷轮盘裂纹扩展特性对比分析

为达到应用人工内部缺陷获得轮盘裂纹扩展特性，开展了含天然与人工内部缺陷轮盘高速旋转低周疲劳裂纹扩展对比试验，并通过无损检测分析、断口分析研究了裂纹扩展特性的差异，提出了含人工缺陷轮盘损伤容限分析思路。无损检测更易识别人工内部缺陷的特征及其变化；人工缺陷区呈碎裂状，有大量的晶间断裂，与天然缺陷区有明显差异；非缺陷区两者无明显差异。天然与人工缺陷区的裂纹扩展速率分别为0.2-0.4μm/次、0.6-1.2μm/次，均远大于基体材料理论值；1#盘加载突变区外断口反推寿命与第二加载阶段循环数的最大误差是12%；2#盘缺陷区外断口反推寿命占总循环数的44.9%-51.9%。基于人工缺陷区定义初始裂纹，排除人工与天然缺陷差异的影响，可获得轮盘裂纹扩展特性。     

Shape control of spacecraft formation using a virtual spring-damper mesh

This paper derives a distance-based formation control method to maintain the desired formation shape for spacecraft in a gravitational potential field. The method is an analogy of a vir-tual spring-damper mesh. Spacecraft are connected virtually by spring-damper pairs. Convergence analysis is performed using the energy method. Approximate expressions for the distance errors and control accelerations at steady state are derived by using algebraic graph representations and results of graph rigidity. Analytical results indicate that if the underlying graph of the mesh is rigid, the convergence to a static shape is assured, and higher formation control precision can be achieved by increasing the elastic coefficient without increasing the control accelerations. A numerical exam-ple of spacecraft formation in low Earth orbit confirms the theoretical analysis and shows that the desired formation shape can be well achieved using the presented method, whereas the orientation of the formation can be kept pointing to the center of the Earth by the gravity gradient. The method is decentralized, and uses only relative measurement information. Constructing a distributed virtual structure in space can be the general application area. The proposed method can serve as an active shape control law for the spacecraft formations using propellantless internal forces.     

分叉尾喷管气动性能实验研究

某涡轴发动机尾喷管由环形转接段和双管急弯收扩段组成，其形状呈“裤衩”形。在模拟涡轮出口旋流的条件下进行了喷管模型内流气动试验，采用双向总压探针测量喷管内大回流区，发现从３３°截面开始的大分离区对喷管性能有重大影响。在给定流量条件下，通过该流量的喷管进出口压比Ｐ＊５／Ｐ６远比无分离的理论值要高。试验证明导流板是减少喷管气流分离、提高扩压比、降低进口总压的有效措施。Ｐ＊５／Ｐ６可降低１．７％左右。