An improved procedure for manufacture of 3D tubes with springback concerned in flexible bending process

Three dimensional (3D) tubes, which possess the characteristics of space saving, lightweight and high strength, are widely used in many high-end industries such as aviation, aerospace, automobile and shipbuilding. However, when manufacturing a 3D tube in flexible bending process, springback is a big obstacle for improving the forming quality. In this paper, a new comprehensive strategy for springback control of 3D tubes is proposed. The strategy can be described as follows: (1) define the desired shape and manufacture shape; (2) optimize the manufacture shape using two tooling design methods (e.g. DA (displacement adjustment) method and B&T (bending and twisting) method presented in this paper); (3) make a discretization of the manufacture shape to acquire the optimized forming parameters. Additionally, experiment is implemented to validate the effectiveness of the new strategy. Results show that forming parameters acquired by the new strategy are partially effective. The new strategy also demonstrates that, during 3D tubes forming, the deviation caused by over-bent elements can be counteracted by the deficient-bent elements. This principle is helpful to reduce the difficulty of parameter determination in future.     

丁羟推进剂伸长率主曲线形状的研究

给出了丁羟推进主要曲线的典型结果，针对其中的一些现象，提出了描述基拉焦形行煌双模量模型和描述其拉伸破坏行为规律的韧性断过程模型。     

降低热变形的卫星有效载荷安装结构优化设计

在整星有限元热变形分析基础上,以有效载荷安装结构热变形最小为目标,对安装结构依次进行拓扑优化及设计敏度分析和尺寸优化。结果表明：通过优化设计,在显著降低该结构热变形的同时大幅减小其质量;拓扑优化给出结构基本构型,尺寸优化进一步细化结构设计方案,二者结合能有效改进结构设计。     

双向阶梯式矩形板的自由振动

本文采用Reisaner—Mindlin一阶剪切变形板理论，得出n级双向阶梯式矩形板自由振动系统的总位能。通过Raylcigh-Ritz法，采用粱函数作为各种边界条件下阶梯式板的位移函数，求得阶梯式板的自振频率。     

基于形状改变比能和材料属性离散的焊接残余应力估算

为了提高焊接残余应力测量精度,在2219-T87铝合金TIG焊接接头残余应力测定试验基础上,通过离散接头材料属性并利用形状改变比能对焊接残余应力进行塑性修正,分别研究孔边塑性变形和接头强度不匹配对焊接残余应力估算的影响。结果表明：同时考虑孔边塑性变形和接头强度不匹配因素的焊接残余应力估算方法,比线弹性残余应力计算方法能最大减小39.8%的误差;当测量点距焊缝距离小于8mm时,在考虑孔边塑性变形的情况下,同时考虑接头不匹配的影响相比不考虑其影响可最大减小40.6%的误差;当测量点距焊缝距离大于8mm时,可忽略接头强度不匹配对焊接残余应力估算的影响。     

碰摩双转子系统弯扭耦合振动分析与实验

针对航空发动机双转子系统,利用拉格朗日方程建立了含碰摩力的弯扭耦合动力学方程,采用龙格-库塔法进行数值计算,结合瀑布图、频谱图、分岔图、庞加莱截面图、幅频曲线分析了弯曲振动和扭转振动的频谱特征和分岔特性;利用增量式编码器对转子实验台进行了扭转振动测量,验证了数值计算得到的频率特征。研究结果表明:弯扭振动具有相似的特征频率,包括倍频、分数倍频、工作频率与倍频/分数倍频的组合频率,但扭转振动的特征频率更加明显;两者还具有相似的分岔过程和相同的分岔点,在每个分岔点处都存在幅值跳跃现象。      

大塑性变形时裂纹稳定扩展的有限元模拟计算

采用8结点等参元并在裂纹尖端采用三角形奇异元对三点弯曲试样在单调加载过程中的裂纹扩展进行了有限元模拟计算。并与实验结果进行了对比。     

基于透射原理的液面变形测量方法综述

带液体燃料的航天器的液体晃动与运动控制离不开液面变形的精确测量。然而液体的弱反射性、易变形性、强透射性等特点增大了液面变形的测量难度,而传统的固体形貌光测技术并不适用。文章综述了目前应用较广的基于透射的液面变形测量方法,重点对相位偏折法、畸变分析法和光线追踪法的测量原理、灵敏度、适用范围和各自的优缺点进行讨论;并展望液面测量方法的发展方向和趋势。     

Study on the Deformation Behavior of Mg-Gd-Y-Zn-Mn Wrought Magnesium Alloys by Visco-plastic Self-consistent Modeling

The plastic deformation behavior of new Mg-Gd-Y-Zn-Mn magnesium alloys gains great necessity to clarify and understand the mechanism deeply. In the present work, the tensile mechanical property test and visco-plastic self-consistent (VPSC) model are used to investigate the activities of deformation modes of VW84M and VW94M magnesium alloys during the tensile deformation. The results show that the mechanical properties of the above extruded alloys are similar but VW94M has higher strength than VW84M after the same aging process. Compared with the extruded alloys, the as-aged alloys have significantly higher activation of pyramidal slip at the later stage of plastic deformation. In addition, the as-aged VW94M alloy with higher strength has the largest activity of pyramidal slip. In summary, the addition of Gd increases the critical resolved shear stress (CRSS) in each slip system of VW94M, while the increase in the strength and the decrease in the elongation of as-aged alloys are associated with the significant activation of pyramidal slip.     

基于归一化参数模型的涡轮盘和涡轮叶片蠕变分析

为完整描述构件3个阶段的蠕变变形计算,结合所发展的各向同性材料的归一化参数蠕变模型,进一步拓展到正交各向异性材料的归一化参数蠕变模型并进行适用性验证。应用所编制的子程序对高温材料涡轮盘和定向结晶材料涡轮叶片结构,进行了蠕变变形及应力松弛效应计算分析。结果表明：经过一定时间的蠕变变形,涡轮盘和涡轮叶片的高应力区会出现应力松弛。总体上轮盘的应力分布更加均匀,静力分析得到的轮盘中心孔、螺栓孔边和轮缘辐板过渡段处高应力区,由于存在蠕变变形,均出现较明显的应力松弛,但是盘中心孔处的应力松弛幅度较小,可能长时间处于高应力状态,应作为结构设计的危险部位重点考查;涡轮叶片也具有同样的应力松弛蠕变效应,特别是随着蠕变变形的增大,叶尖径向变形(位移)逐渐增大,在结构设计中,应考虑叶片叶尖与机匣长期工作径向碰摩而带来的不利影响。