2020级

硕士毕业论文

论文题目：大型CFRP薄壁管加劲环稳定性能研究
硕士研究生：米翔
指导老师：陈务军 教授
摘要
       平流层飞艇作为一种新型绿色飞行平台，对龙骨结构具有超大超轻的设计要求。随着制造技术的快速发展，碳纤维复合材料凭借高韧性、优异的抗疲劳和抗氧化性、优异的耐磨性、轻质高强等特性被广泛地应用在航空航天、土木工程、新能源产业等诸多领域。本文所研究的平流层飞艇创新性地将CFRP轮辐式张拉结构（加劲环）作为飞艇骨架的关键结构部件之一，实现了刚柔一体结构的轻量化设计，同时保证了足够的结构刚度。然而新的结构形式和新的材料应用，加之超大结构尺度，意味着更高的制造水平、更大的集成难度和更精确的安装要求。对于CFRP加劲环，从制造、集成到安装，整个过程结构都有面临失稳破坏的风险，尤其是在集成阶段，张拉索力的确定至关重要。所以需要对结构的稳定性能有足够的认识，才能防止结构发生意外的失稳破坏。基于此，本文针对两类大型CFRP薄壁管加劲环的稳定性能做了充分的研究。
      首先，对单管加劲环的稳定性能进行有限元分析。以两个相同构型不同直径的单管加劲环为例，对结构的初始构型和不同张拉位移下的构型进行特征值屈曲分析，发现结构的稳定性能存在一个最优值；对结构进行非线性屈曲分析，研究了初始预应力的影响，并对临界屈曲索力的定义做了分析，考虑初始几何缺陷等因素得到了较为真实的结构的临界屈曲荷载；对两个不同直径的单管加劲环做了比较，发现直径增大后，加劲环的临界屈曲荷载明显降低；此外，针对材料参数、结构几何尺寸等因素做了参数分析。
        然后，对桁架加劲环的稳定性能进行有限元分析。针对桁架加劲环，同样模拟结构的集成过程，研究了不同张拉位移下的稳定性能变化，发现对于整体屈曲模态，结构的稳定性能同样存在最优值；并对预张拉工况和固定毂轴长度工况做了详细的非线性屈曲分析，得到了结构临界屈曲荷载；考虑初始几何缺陷，研究了不同缺陷形式和缺陷幅值下的结构稳定性，发现结构对于初始几何缺陷的分布形式和幅值大小较为敏感；同时针对材料参数和几何参数进行了相应的参数分析。
        最后，对桁架加劲环标准节段的稳定性进行试验研究和有限元分析。模拟节段的受力工况，进行了极限承载力破坏试验；得到了结构的破坏模式、极限承载力、刚度表现以及关键杆件和节点的应变发展情况；考虑复合材料铺层对节段进行精细化建模，对试验结果进行验证，同时进一步对弦杆、腹杆和节点套管进行应力分析，发现有限元可以较好的模拟结构的极限承载力和变形情况；最后针对初始几何缺陷和铺层设计进行了参数分析研究，用于提高仿真精度和后期的结构设计优化。
关键词：平流层飞艇，CFRP薄壁管加劲环，特征值屈曲，非线性屈曲，几何缺陷分析，极限承载力试验

STABILITY OF LARGE CFRP THIN-WALLED PIPE STIFFENING RING

Abstract: Stratospheric airships, as a new type of green flight platform, have the structural design requirement of extra-large and ultra-lightweight keel structures. With the rapid development of manufacturing technology, carbon fiber reinforced resins are widely used in aerospace, civil engineering, and new energy industries with high toughness, excellent fatigue, and oxidation resistance, excellent temperature wear resistance, and light weight and high strength. The stratospheric airship studied in this paper innovatively uses CFRP spoke tensioning structure (stiffening ring) as one of the key structural components of the airship skeleton, which realizes the lightweight design of the rigid-flexible structure and ensures sufficient structural stiffness at the same time. However, the new structural form and new material application, combined with the large structural scale, means a higher manufacturing level, greater integration difficulty, and more precise installation requirements. For CFRP stiffened rings, the structure is at risk of destabilization failure throughout the process from fabrication, and integration to installation, especially during the integration phase when the determination of the tensioning cable force is critical. Therefore, it is necessary to have sufficient knowledge of the stability performance of the structure to prevent accidental destabilization failure. Based on this, the stability performance of two large CFRP thin-walled pipe stiffening rings is fully investigated in this paper.
        Firstly, the stability performance of the single-pipe stiffening ring is analyzed by finite element analysis. Taking two single-pipe stiffening rings of the same configuration with different diameters as an example, an eigenvalue buckling analysis was performed for the initial configuration of the structure and the configuration under different tension displacements, and it was found that an optimal value of the stability energy of the structure exists. A nonlinear buckling analysis was performed on the structure, the effect of initial prestress was studied, and the definition of critical buckling cable force was analyzed, and a more realistic critical buckling load of the structure was obtained by considering the initial geometric imperfections and other factors. The critical buckling load of the stiffening ring was found to be significantly reduced by increasing the diameter of the single-tube stiffening ring for two different diameters. In addition, parametric analysis was done for material parameters, structural geometry and other factors.
        Then, the stability performance of the truss stiffening ring was analyzed by finite element analysis. For the truss stiffener ring, the integration process of the structure is also simulated, and the stability performance changes under different tension displacements are investigated, and it is found that the optimal value of the stability performance exists for the overall buckling mode. A detailed nonlinear buckling analysis is also done for the pre-tensioning condition and the fixed hub axis length condition, and the critical buckling load of the structure is obtained. Considering the initial geometric imperfections, the stability of the structure under different imperfection forms and imperfection amplitudes is studied, and it is found that the structure is sensitive to the distribution form and amplitude of the initial geometric imperfections. The corresponding parametric analysis is also carried out for the material and geometric parameters.
        Finally, experimental study and finite element analysis of the stability of the standard section of the truss stiffening ring are carried out. The ultimate load capacity failure test was carried out to simulate the force conditions of the section. The failure mode, ultimate load capacity, stiffness performance and strain development of key pipes and joints of the structure were obtained. Refined modeling of the section considering composite layup was carried out to verify the test results, while further stress analysis of the chords, webs and sleeves was carried out, and it was found that the finite element could better simulate the ultimate load carrying capacity and deformation of the structure. Finally, a parametric analysis study was carried out for the initial geometric imperfections and the layup design, which was used to improve the simulation accuracy and the later structural design optimization.
Key words: stratospheric airships, CFRP thin-walled pipe stiffening rings, eigenvalue buckling, nonlinear buckling, geometric imperfection analysis, ultimate load capacity test

论文题目：SMPC圆管及可展桁架力学特性试验与分析
硕士研究生：王晓情
指导老师：陈务军 教授
摘要

         形状记忆聚合物复合材料（Shape Memory Polymer Composites, SMPC）是一种在航天领域具有应用潜力的智能材料，基于SMPC形状记忆效应的大型空间可展桁架阵面天线，通过SMPC圆管构件的形状记忆性能实现折叠和展开。SMPC可展桁架须在地面进行重复折叠展开形状记忆历程以及系统功能试验后，再发射入轨，因此，对于历经重复折叠后SMPC构件和桁架性能的研究是工程亟需解决的关键问题。本文针对大型SMPC可展桁架阵面天线的技术需求和工程背景，对SMPC圆管构件及其可展桁架进行力学特性试验和分析，主要内容包括：
        以展开态SMPC圆管为研究对象，进行展开态SMPC圆管扭转试验，探究SMPC圆管悬臂边界下的剪切性能，评估圆管特殊制作工艺对材料性能的影响。对历经重复折叠展开后的SMPC圆管开展悬臂和自由边界条件下的模态试验与分析，总结模态规律，采用动态法测得每根圆管的等效刚度特性。进行展开态SMPC圆管折叠损伤影响探究试验，开展悬臂边界下的模态试验，总结折叠对圆管动态力学特性的影响规律，为圆管折叠操作工艺提供指导。
        以折叠态SMPC圆管为研究对象，对展开态圆管升温折叠，得到V形和Z形两种折叠形态，通过模态试验研究两种折叠形态SMPC圆管的动力学特性，考虑了端部支承约束对动力学特性的影响，以模拟折叠形态SMPC圆管在发射阶段整流罩内安装锁定状态。仿真模拟了展开态圆管的折叠过程，得到折叠态圆管有限元模型，求解的模态参数与试验结果吻合较好。参数化研究了端部支承约束对动力特性的影响，发现水平和竖直方向上施加弹簧单元能有效提高该方向的整体弯曲刚度。
        以SMPC可展桁架阵面天线为研究对象，为探究经历重复折叠展开形状记忆历程后的SMPC桁架动态力学性能，开展了重复折叠后五节SMPC可展桁架地面模态试验，得到自由边界下的模态特征，探究阵面板和预应力索对桁架结构模态参数的影响。结果表明，预应力索可提高桁架的整体刚度，并且提高了沿纵向的抗剪能力，而阵面板可提高桁架的扭转刚度。建立了考虑空气阻力效应的有限元模型，进行数值模拟，仿真结果与试验结果吻合较好。其次，考虑实际大型星载天线的应用需求，系统开展了五节和十八节SMPC可展桁架折叠态的模态仿真分析，分析了管端弹簧约束对结构动力学性能的影响。开展三十六节桁架动态力学特性仿真研究，对目标天线的总体设计具有一定参考价值。
         最后对全文工作进行总结，并提出未来研究展望。