Mechanical analyses of “Shellular”, an ultralow-density material

Recently, a new ultralow-density material composed of continuous shells called “Shellular” was introduced. Shellular has the typical hierarchical architecture across multiple scales, and its constituent material is a plated metallic film with nano-sized grains, providing a high extent of strength well over 1 GPa. Furthermore, Shellular is expected to overcome the problems caused by the geometrical incompleteness, stress concentration, and flaws or imperfections that were often found in previous ultralow-density materials composed of hollow trusses. This work evaluated the mechanical properties of the Shellular subject to compression using theoretical and numerical analyses comprised of two stages. The results revealed that the fillet size at the openings is a critical parameter, and that local buckling due to the geometric unevenness of the shell occurs immediately upon the load applied, which accelerates the consequent overall failure. Hence, to obtain higher properties, particularly in ultralow-density domain less than 10−2 g/cc, local buckling must be suppressed through an evening and smoothening of the surfaces over the entire shell.