Comparison of the mechanical performance of architected three-dimensional intertwined lattices at the macro/microscale

The design of lattice structures with exceptional mechanical performance has been accentuated by recent advances in both additive manufacturing and mechanical modeling. Although there is a plethora of different lattice structures with intriguing properties, such as auxeticity and reciprocity, an exceptional class of lattice geometries is that of intertwined lattices, designed by the tactical coalition of polyhedral structures. Although the superior mechanical performance of the latter structures has been demonstrated at the microscale, their mechanical analysis is still incipient. In this study, the design principles and mechanical performance of such three-dimensional structures were examined at the macroscale and juxtaposed with their microscale counterparts. As a proof of concept, the first stellation of the rhombic dodecahedron, an ultralight/ultrastiff architected structure with superior stiffness and strain hardening characteristics, was examined both numerically and experimentally. Finite element analysis showed that intertwining greatly enhances both the stiffness and isotropic behavior of the structure. In addition, mechanical testing of both microscale and macroscale structures revealed that lattice intertwining leads to commensurate stiffness and strain energy density compared to that of the bulk material, even for 20% relative density. The findings of this study pave the way for a systematic and rigorous approach to design and modeling of macroscopic intertwined geometries, for comparing them with their microscopic equivalents, and for providing insight into scale effects on the mechanical performance of architected materials with intertwined lattices.