基于SLM的应力匹配变密度轻质金属点阵结构设计理论及实验研究

The demand for lightweight structures in large aerospace equipments and metallic lattice structure fabricated by SLM is growing rapidly. However, the mechanical properties of lattice structure, its optimization methods and key factors which affect the working accuracy during SLM are still not clear at present. In this project, we will analyze the metallic lattice structure, macro and micro mechanical properties of the novel variable-density lattice structure under different loading conditions with the microstructure design method and the AM technique. Then a new optimization method and a multi-scale FEM of variable-density lattice structure are proposed, in which topologies and dimensions of units are matched with different stress conditions. Moreover, coupling effects of several factors which influence the molding quality of structures during the SLM process are studied. To verify our simulations, a series of mechanical experiments are conducted to compare mechanical properties of the simulated structure and other typical lightweight structures. The results show that a full complement of design and test methods of the novel lightweight stress-matched lattice structure is established, which is able to provide theoretical support to the optimization design and manufacturing of lightweight microstructure in metal parts. Our research not only benefits the aerospace and automobile industries but also profits other lightweight-demanding fields.

面向航空航天产品轻量化的巨大需求，针对目前轻质金属点阵结构力学特性与结构优化研究尚需完善及SLM成型过程中多种因素对点阵结构精确成型的耦合效应不明确等问题，以金属点阵结构为研究对象，以金属点阵结构和增材制造技术为基础，综合理论分析、数值模拟和实验研究等技术手段，建立具有应力匹配特性的变密度轻质金属点阵结构模型，研究其在多种载荷条件下的宏观和微观力学特性，提出基于遗传算法的应力匹配变密度点阵结构自适应结构优化设计方法，揭示SLM过程中影响金属点阵结构精确成型因素的耦合机理，完成与典型轻质结构的力学性能对比实验，形成一整套关于应力匹配变密度轻质金属点阵结构的设计理论和实验方法，为我国航空航天及汽车等领域轻质金属构件内部多孔结构设计与制造提供理论和使能技术支撑。

针对目前轻质金属点阵结构力学特性与结构优化研究尚需完善的问题，研究了点阵结构在准静态单轴压缩环境下的力学响应，建立了针对定密度及变密度体心构型点阵结构普遍适用的力学分析方法；建立了针对复杂点阵结构静力学特性的数值模拟方法；在此基础上，针对体心构型点阵结构所存在的轻质化与承载能力间此消彼长的矛盾，提出了体心四方（Body-centered Tetragonal；BCT）点阵结构的一般模型，并基于点阵结构构型尺寸的多目标优化算法及理想点法求解得到了BCT点阵单胞综合最优构型尺寸；提出了具有应力匹配特性的基于消除点阵结构单胞结点应力集中的变密度结构；提出了基于萤火虫算法、基结构法的拓扑生成算法。针对SLM成型过程中多种因素对点阵结构精确成型的耦合效应不明确的问题，探讨了在SLM加工过程中不同扫描速度、激光功率、扫描时间间隔及粉末颗粒大小对成型样件性能的影响，实现了SLM制备过程参数的最优化；建立了针对消除样件应力集中的后处理过程。最后，进行准静态单轴压缩实验，研究了点阵结构在准静态受载环境下的破坏模式、机理，提出了结合结构拓扑优化的无支撑结构设计方法理论，完成了六种轻质点阵结构的力学性能对比实验，验证了针对点阵结构所提出的理论、方法的有效性和真确性，形成了一整套关于应力匹配变密度轻质金属点阵结构的设计理论和实验方法。为我国航空航天及汽车等领域轻量化金属构件设计与制造提供了理论和使能技术支撑。