选择性增强铝锂合金航空整体壁板的止裂机理与损伤容限设计

Manufacturing of high-performance integral structures has been developed as the most effective method to reduce aircraft’s weight and manufacturing costs. However, integral structure itself cannot effectively prohibit crack propagations, which greatly influence damage tolerance. To solve such a problem, new conceptual design method of selective reinforcement is now regarded as the most important technology. Since the complexities of damage analysis and interface performance exist, neither have hybrid damages caused by fatigue crack, delamination or buckling of the selective reinforced integral structure been suppressed, nor has the low reliability of the adhesive strength been solved effectively. Hence, such problems have greatly influenced residual strength and service safety of the structure.. Taking integral aluminum-lithium aircraft panels for research object in this project, researches are systematically carried out, which include selective reinforcement structures design, mechanism and stability study of bond process, damage forecast and performance evaluation of certain new conceptual structure. Firstly, based on the performances research of bonding interface (include interface wetting, plying, texture evolution and etc.), bonding mechanism is revealed and a reliable bonding process with high consistency strength is formed. Then, a hybrid damage analysis technology, which consists of cohesive zone modeling and extended finite element method (CZM/XFEM)), is proposed to reveal mechanisms and conditions of crack turning and buckling of the selectively reinforced integral panels. Finally, influences of connection methods, bonded strap’s geometry parameters, and curing cycle on the performances of reinforced panel’s comprehensive strength, crack propagation and remaining useful life are studied, and relevant performances optimization are carried out. Such researches will boost damage tolerance design and comprehensive characteristic evaluation for selective reinforced integral panels.

设计制造大型整体构件是飞机减重与降低成本的重要手段，但整体结构自身无法抑制裂纹扩展，难以满足损伤容限要求，选择性增强是有效解决该问题的关键技术。但选择性增强整体结构的疲劳断裂、界面分层、失稳破坏等混合损伤及粘接强度的低可靠性问题一直未能有效解决，严重影响了结构的剩余强度和服役安全性能。. 项目以铝锂合金航空壁板为研究对象，开展选择性增强整体壁板的结构设计、粘接机理与稳定性工艺、损伤预测与整体性能评估等方面的研究。基于界面润湿、铺层扩展及织构演变等连接界面的性能研究，揭示粘接增强机理，形成高一致连接强度的粘接工艺；建立选择性增强结构的界面元-扩展有限元复合建模的混合损伤分析方法，揭示裂纹转折的机理、条件与失稳机制；开展增强方式、结构参数、固化制度等因素对整体壁板综合强度、裂纹扩展和剩余寿命等参数的影响研究与性能优化，实现选择性增强整体壁板的综合性能评估与高损伤容限设计。

项目以航空用铝锂合金选择性增强整体壁板为研究对象，针对选择性增强结构的粘接工艺与胶接机理、选择性增强结构对裂纹扩展的抑制机理与优化设计、选择性增强结构的剩余寿命预测与延寿方法、选择性增强结构的损伤预测与力学性能评估、以及湿热环境下选择性增强胶接结构强度的退化机制与强度预测等方面开展研究。.项目研究的主要内容包括：.1）研究了不同表面处理方式下铝锂合金/FM94胶接接头粘接强度的变化规律，揭示了不同表面处理方式下粘接界面形貌、化学成分、润湿性能、以及织构演变等界面性能对接头强度的影响规律，发现机械啮合与粘接吸附为粘接增强的主要机制。在此基础上，提出了喷砂与阳极化相结合的表面处理方式，优化了粘接工艺参数，形成了高一致连接强度的粘接工艺，粘接接头剪切强度超40MPa。.2）提出了基于交互积分的选择性增强结构界面元-有限元（CZM/FEM）及界面元-扩展有限元（CZM/XFEM）复合建模方法，实现了动态疲劳及冲击载荷下选择性增强结构胶接损伤-裂纹扩展-疲劳寿命的统一预测，揭示了选择性增强结构对裂纹扩展抑制的机理与条件。.3）开展了选择性增强方式、增强结构几何与位置参数等因素对选择性增强结构裂纹扩展和剩余寿命等参数的影响研究与性能优化，提出了选择性增强结构的优化设计与片前开孔促使裂纹转折的选择性增强结构延寿与损伤容限优化设计方案：矩形选择性增强补片相对宽度为35.6%、相对长度50%、相对厚度为83.3%；孔洞相对半径2.22%、相对轴向距离4%、相对水平距离15.56%时，延寿与促进裂纹偏转的效果较好。.4）开展了选择性增强结构的拉剪强度、弯曲强度、抗冲击性能及其在复合载荷下的压缩失稳与极限强度评估等方面研究，开发了考虑初始几何缺陷（由固化应力等因素造成）的整体加筋壁板极限强度参数化建模与分析的软件平台。.5）开展了服役条件下选择性增强结构的耐久性实验与机理研究，基本查明了胶接强度的退化机制与耐久性原理，为选择性增强结构的长期安全服役与损伤容限评估提供了理论与数据支撑。