Composite strut-plate lattice: A high-stiffness design of cellular metamaterial having excellent strength and energy absorption ability

Abstract

Although the 3D-printed plate lattices have higher stiffness and strength than the strut lattices, the difficulty in fabricating the plate microlattices limited their potential application. The plate lattices require holes in the plates to remove the powder trapped inside, but introducing holes in plates in a lattice could reduce stiffness and strength. In general, to enhance the mechanical properties of a specific lattice for a particular mass, the size of the unit cell should be reduced. However, small plate unit cells require tiny holes on plates that may not be sufficiently large enough for post-fabrication powder removal. Thus, as an alternative design strategy, this work proposes a composite strut-plate lattice inspired by fiber-reinforced composite materials to achieve high stiffness, strength and energy absorption ability. Further, this study provides a methodology based on the classical rule of mixture for composite materials to determine the threshold volume fraction of the plate lattice reinforcement in the strut lattice matrix to attain a stiffness value that exceeds the maximum theoretical stiffness limit— the Hashin-Shtrikman upper bound. The finite element simulation results were corroborated by quasi-static compression tests on 3D-printed lattices made of polymer PA12 fabricated using multi jet fusion technique. Notably, the yield strength of the lattice exceeded the maximum theoretical yield strength limit— the Suquet upper bound. Also, the energy absorption ability was remarkably improved compared to the strut lattice and was close to that of the plate lattice. • Combined strut and plate unit cells that solve 3D printing's powder entrapment problem. • Stiffness and yield strength beyond their theoretical limits are achieved. • Mechanical properties are tailored using composite rule of mixture. • The designed composite lattice shows excellent energy absorption ability. • Mechanical properties are predicted by FEM and corroborated with experiments.