# Space Node Topology Optimization Design Considering Anisotropy of Additive Manufacturing
###### Abstract
It is important for the nodes to be stronger than the rods in the space structure; otherwise, the damage to nodes will cause extensive collapse as they are connected with many rods. In addition to being lightweight, topology-optimized space nodes will have greater stiffness, meeting this requirement. [PERSON] et al. [17; 18] carried out topology optimization of maximum stiffness and minimum mass for cable-rod nodes in space structures. [PERSON] [19] studied the optimization and additive manufacturing of bifurcated cast steel joints. [PERSON] [20] took the spherical node as the research object and compared the mechanical properties of multi-objective optimization and single-objective optimization. [PERSON] [21] used the over-section method and the BESO method to study the topology optimization design of a six-bar box node in Sunshine Valley. These studies have greatly broadened the application scope of additive manufacturing and topology optimization, as well as accelerated the continuous innovation of manufacturing technology and industrial applications. It should be noted that it is also necessary to consider the anisotropy problem caused by additive manufacturing in the application research of topology optimization for additive manufacturing, concerning components that require stiffness, especially space nodes with complex forces. The general topology optimization only considers isotropic materials, which ignores the anisotropy caused by the manufacturing process. Numerous articles have pointed out that anisotropy is common when most materials are used in additive manufacturing, where the mechanical properties of the manufactured components are almost different in all directions. [PERSON] [22] conducted tensile and compression tests in different directions on specimens made of PLA, which showed strong anisotropy in the test. In addition to PLA materials, AM specimens of other polymer materials, such as ABS [23], polypropylene [24], and polycarbonate [25], also showed anisotropy in the experiments. With regard to the anisotropy of metal materials, researchers have mainly studied 316 Lstainless steel. [PERSON] [26], [PERSON] [27], and [PERSON] [28] studied 316L stainless-steel specimens prepared by selective laser melting. Studies found that the metal specimens also had anisotropy, with the mechanical properties in the manufacturing direction being the weakest. The microstructure of the samples also showed grains with directional characteristics. Furthermore, the same was true in terms of microstructure. [PERSON]'s [29] studies on topologically optimized microstructures showed that the additive manufacturing of microstructures also has anisotropic behavior. [PERSON] [30] proposed a gradient-based algorithm to simultaneously optimize the microscale structures and macroscale material properties, and the high computational efficiency and superior structural mechanical properties of the orthotropic porous material were experimentally demonstrated. Therefore, it is necessary to consider the anisotropy caused by the manufacturing process in the optimization and manufacturing process. Using the Abaqus solver and Matlab programming, this paper integrated an optimization platform for topology optimization and conducted an additive manufacturing mechanical test with 316L stainless steel as the research object to study the mechanical properties of the material in different directions. The elastic constants in different directions obtained from the experiment were used as anisotropic material properties for optimization research. In the optimization analysis, the anisotropic parameters are respectively substituted into the model optimized by the isotropic parameters for calculation, to analyze the mechanical properties of the isotropically optimized nodes in different directions during manufacture. In addition, unlike the general isotropic study, this paper also input the anisotropic parameters before topology optimization.