Constrained functionally graded gyroid structure for tunable energy absorption

• Graded gyroid with wall constraints are proposed for energy absorption. • Outer wall improves load transfer, delaying collapse and densification. • Energy absorption improves up to 240% with combined grading and confinement. • Dual-objective design optimizes both crash absorption and force-limiting behavior. • Experimental and numerical results confirm performance under compressive loading. Gyroid metamaterials are promising for impact mitigation due to their high surface-to-volume ratio, smooth stress distribution, and tunable mechanical response. This study examined thirty thermoplastic polyurethane (TPU) gyroid structures produced by 3D printing, comprising equal numbers of simple gyroid (SG) and wall constrained gyroid (CG) structures. Three geometric refinements, defined by the number of unit cells per edge, and five relative density gradients from uniform (0%) to graded (40%) were implemented to enable systematic evaluation under quasi-static compression. Two performance scenarios were defined, a crash-absorption case to maximize absorbed energy and a force-limiting case to minimize transmitted peak load, relevant to applications such as automotive bumpers and wearable protective gear, respectively. Experimental testing validated the finite element simulations, which showed that CG designs achieved up to 240% higher energy absorption and 68% greater specific energy absorption compared to SG designs. Performance maps identified the CG structure with two cells per edge and a relative density gradient of 30% as optimal for energy absorption efficiency, providing actionable design rules for next-generation impact-mitigation metamaterials.