Stepwise graded struts for maximizing energy absorption in lattices

Increasing the energy absorption capability of lightweight structures without reducing stiffness and strength has been a long-standing challenge, as numerous applications exist with potentially great impact. Particularly, in volume or weight restricted environments, such as cars, helmets or packaging, the performance, safety, cost, and environmental impact is substantially affected. However, these properties are typically found only in nature. We propose a novel architectural paradigm that adds stepwise graded core-shell struts to bending dominated lattices to increase energy absorption up to 38 times with negligible changes in density or mass, i.e., less than +2.5%. We optimize the material in each coaxial layer for maximum toughness and, enabled by multi-material 3D printing, validate the results experimentally for single struts, unit cells, and lattice structures. The bio-inspired and highly versatile architectural paradigm is scale-independent, locally tunable, applicable to different lattice cell types and geometries, and, therefore, applicable to a wide range of mechanical meta-materials and structures. (C) 2018 Elsevier Ltd. All rights reserved.