Multiscale structural design of columns made of regular octet-truss lattice material

This paper focuses on the structural design of the microscopic architecture of a lattice material with regular octet-truss cell topology and on the multiscale design of an axially loaded member manufactured of this type of cellular solid. The rationale followed here hinges on the coincidence of the failure modes of a stretching dominated lattice material, which experiences two types of microscopic failure modes, namely, elastic buckling and plastic yielding. A lattice material that fails by the elastic buckling of its cell elements without reaching the plastic yielding is far from optimum. To avoid this event and improve the material strength, we first start to tailor the structural efficiencies of the cell elements. We show that by shaping the cell element cross-sections, the lattice material buckling resistance can increase until it equals the cell element yield strength, thereby exploiting fully the lattice material strength. The coincidence of these two failure modes is the structural criterion used to develop selection charts for the micro-structural design of the octet-truss lattice material. In the second part of the paper, we examine the design of a structural column manufactured by regular octet-truss lattice material. We show that to maximize the structural failure resistance at both the structural and the material levels, the global buckling and the yielding failure of the column must occur simultaneously with the microscopic failure modes of the lattice material, namely the local buckling and the yielding of its microscopic cell elements. The paper concludes by illustrating how the micro-truss geometry and the column cross-section can be simultaneously designed to fully exploit the strength of the material and the overall macrostructure.