Collapse mechanism maps for a hollow pyramidal lattice

Cellular materials with hollow lattice truss topologies exhibit higher compressive strengths than equivalent structures with solid trusses owing to their greater resistance to plastic buckling. Consequently, hollow trusses have attracted interest as the cores for sandwich panels. Finite-element calculations are used to investigate the elastic–plastic compressive collapse of a metallic sandwich core made from vertical or inclined circular tubes, made from annealed AISI 304 stainless steel. First, the dependence of the axial compressive collapse mode upon tube geometry is determined for vertical tubes with built-in ends and is displayed in the form of a collapse mechanism map. Second, the approach is extended to inclined circular hollow tubes arranged as a pyramidal lattice core; the collapse modes are identified and the peak compressive strength is determined as a function of geometry. For a given relative density of hollow pyramidal core, the inclined tube geometry that maximizes peak strength is identified. The predicted collapse modes and loads for the pyramidal core are in excellent agreement with measurements for the limited set of experimentally investigated geometries.