Additively-manufactured metallic micro-lattice materials for high specific energy absorption under static and dynamic loading

An octet truss lattice material is designed for energy absorption purposes featuring an exceptionally high specific energy absorption, a constant plateau stress between initial yield and densification, and zero plastic Poisson's ratio. It is demonstrated through detailed finite element simulations that the meso-structural response of metallic lattice materials under compression changes from an unstable twist mode to a stable buckling free mode at a relative density of about 0.3. Furthermore, it is found that the nature of the macroscopic stress-strain curve changes from mildly-oscillating to monotonically increasing as the meso-structural deformation mode changes, while a stress-plateau is observed at relative densities above 0.3. Since the specific energy absorption is a monotonically increasing function of the relative density, lattice materials of relative densities around 0.3 feature both a plateau stress and a high specific energy absorption capability. Prototype materials are built from stainless steel 316L using Selective Laser Melting. The basic building element of the micro-lattices are 2.2 mm long beams with a 500 gm diameter cross-sections. Detailed micro- and meso-structural analysis including tomography, microscopy and EBSD analysis revealed substantial local material property variations within the lattice structure. Compression experiments are performed under static and dynamic loading conditions confirming the anticipated exceptional energy absorption material characteristics for strain rates of up to 1000/s. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.