Functionally graded lattice structures with tailored stiffness and energy absorption

• Diameter and spatial grading strategies for controlling the relative density. • New analytical model for functionally graded lattice structures. • Tailored stiffness and energy absorption profiles via cell orientation, truss diameter, and cell size. • New optimisation approach for maximising absorbed energy with stiffness constraints. Lattice structures are lightweight and are known to exhibit excellent energy absorbing capability when subject to compressive loading. In this paper, a new analytical model for the stiffness, strength, and energy absorption of additively manufactured functionally graded lattice structures is presented, leading to the establishment of a new energy absorption optimisation approach. The influence of cell orientation, cell aspect ratio, and cell relative density on the mechanical properties is characterised. The optimal through-thickness density distribution to maximise energy absorption is determined, subject to mass and initial stiffness constraints. Energy absorption is shown experimentally to increase by up to 67.1 % via tailored through-thickness grading of the structure's relative density. Finite element models are also developed to accurately describe the mechanical performance of these functionally graded lattice structures. These models provide valuable insight into the properties of functionally graded lattice structures and can serve as a basis for the tailored design of lightweight energy absorbers.