Design and experimental validation of additive manufactured cylindrical metamaterials for load-bearing automotive bumper

This study presents a novel Tubular Chiral Metamaterial Structure (TCMS) and its presented application as a load-bearing energy-absorbing core for automotive bumper systems. Unlike conventional planar chiral or lattice metamaterials, the TCMS integrates periodic chiral unit cells into a tubular architecture, enabling rotational, bending-dominated, and auxetic deformation mechanisms under axial compression. The structures were fabricated using high-resolution Digital Light Processing (DLP) additive manufacturing with an ABS-based resin, ensuring high geometric fidelity and repeatability. A combined experimental–numerical framework was employed to characterize the compressive response, with finite element simulations validated against quasi-static compression experiments, showing discrepancies below 2%. A systematic parametric study was conducted by varying the unit cell wall thickness (0.2–0.8 mm) and chiral circle diameter (2–5 mm) across nine TCMS configurations. The results reveal that wall thickness is the dominant design parameter governing mechanical performance. Exceptional tunability was achieved, with axial stiffness ranging from approximately 42 to 1000 N/mm (≈2280% increase) and specific energy absorption values exceeding 1300 mJ/g, corresponding to more than a 1000% improvement between extreme designs. In addition, the TCMS exhibits a strong and controllable auxetic response, with effective Poisson’s ratios reaching values below −3, leading to enhanced deformation stability, reduced stress localization, and delayed buckling. The presented bumper application demonstrates that the TCMS can simultaneously sustain service-level compressive loads and dissipate impact energy through controlled progressive deformation. These findings establish the TCMS as a high-performance polymer metamaterial bridging the gap between lightweight energy absorbers and structural load-bearing components for next-generation vehicle bumper systems.