Improvement in energy absorption of additively manufactured lattice structures after modification of collapse mechanisms

Collapse mechanism dictates plateau behavior for a lattice. Sharp large drops in this region are due to formation of diagonal shear bands. They may ruin energy absorption capacity of lattice. This paper is an attempt to evaluate the possibility of improving collapse mechanism in favor of energy absorption. A significant number of tests were conducted to investigate the influence and effectiveness of changes in cell topology, solid material properties, and relative density. It was demonstrated that alteration of solid material properties (through heat treatment) as well as relative density can affect fluctuations in the plateau region significantly. This has been possible through replacing shear bands with normal layer failure, or through thickening the shear band and smoothening the transitions. One of the practical achievements for this study is that the best energy absorption performance was obtained at relative density ranging from 20 to 30%. At this range, the specific absorbed energy (energy per unit weight) reaches its maximum peak for all examined lattices. However, magnitude of the peak is highly dependent on the lattice topology. This highlights the superiority of lattices as engineered structures over conventional metallic foams. Among the wide range of examined strut- and surface-based lattices, face-centered cubic (FCC) and Schwarz D lattices performed the best for weight-sensitive energy absorption applications.