Structural behavior of 3D-printed diamond-shaped lattice steel elements

Lattice materials and structures have attracted increasing interest over the years due to their tunable mechanical properties, making them suitable for applications requiring lightweight and adaptable structural elements. However, conventional fabrication techniques through casting or more commonly adopted metal additive manufacturing technologies, such as Powder-Bed Fusion, significantly limited the scalability of such elements. With the advent of large-scale metal 3D printing technologies, such as Wire-Arc Additive Manufacturing (WAAM), lattice structures could be scaled from micro- (at the material scale) to meso-scale (at the structural element scale). The two main features of such meso-scale metal lattice structural elements are the material continuity of the nodes and the absence of any horizontal struts. This research investigates the structural behavior of a new generation of WAAM-produced diamond-shaped lattice steel elements, focusing on their specific mechanical properties and flexural-dominated structural performance under compression loading. The bending moment-governed response opens new potentials to be explored, specifically as low-stiffness elements, flexibility-controlled devices, hysteretic dissipators, shock absorbers, etc. The work provides an overarching study from the conceptual definition to analytical, experimental and numerical investigations on various configurations of 3D-printed diamond-shaped lattice steel elements. First, the study introduces the concept of diamond-shaped lattice elements, describing their grammar from the elementary unit (D-Chip) to larger assemblies such as D-Planes, D-Surfaces, and D-Poles. Then, an analytical formulation of the yielding capacity of D-Poles under compression is developed, considering both planar and spatial behaviors. Finally, experimental tests are carried out on various configurations of WAAM-produced D-Poles, and numerical simulations are developed through Finite Element (FE) modeling on different idealizations of the printed geometry. The main results lie in: (1) the analytical understanding of the structural behavior, with simple analytical formulas that could assist the designer in the preliminary sizing of these elements; (2) the identification of two regions within the D-Poles, namely the boundary and internal ones, characterized by different static responses, with major influences on shorter D-Poles; (3) the need for proper geometrical modeling able to capture the real printed geometry of the D-Pole, characterized by line-nodes rather than point-nodes, which affect the structural response under compression loading. The results also demonstrate that diamond-shaped lattice elements exhibit high deformability due to the mainly flexural behavior and variable yielding capacity depending on the tessellation of the D-Pole, significantly affected by its number of faces.