Graded lattice structures: Simultaneous enhancement in stiffness and energy absorption

Distinguished capabilities of cellular solids as high-performance energy absorbers can be enhanced by engineering their underlying architectures. In this study, we classify different groups of lattices based on their topology and propose a strategy to enhance their energy absorption-to-weight ratio under compression. We particularly elucidate the effect of variation of relative density across the lattice structures 3D printed by stereolithography. The experimental compression test results and numerical data obtained by finite element analysis show that a uniform design with even distribution of relative density yields the highest initial stiffness among all 3D printed architected lattices. However, the graded design with a rational variation of relative density can significantly enhance the stiffness and energy absorption capability of lattices experiencing high compressive strains. Specific gradients, where the relative density varies normal to the direction of external compressive force, can increase the stiffness and the energy absorption capabilities of cellular solids up to 60 and 110%, respectively. These results promise the possibility of designing single-phase lattice architectures that can combine lightweighting and energy absorption properties by a rational variation of porosity within the cellular architecture.