Greek key-inspired fractal metamaterials with enhanced flexibility and energy absorption.

Architected materials with intricate three-dimensional (3D) geometries offer unique properties and functionalities but face challenges in manufacturing costs and complexity. This research explores the integration of simple 2D Greek Key-inspired lattices into fractal designs to achieve exceptional mechanical performance. Using 3D printing and kerfing, these fractal structures demonstrate enhanced flexibility and energy absorption capabilities. Through three-point bending and in-plane tensile tests, the 2D fractal lattices exhibited a 600-fold reduction in bending force and a tensile stretch capacity of up to 520%, significantly outperforming brittle parent materials. Out-of-plane compression tests revealed a five-fold increase in energy absorption compared to honeycomb structures, further enhanced by alternating stiff and soft multi-layered designs. Advancing to 2.5D tubular and 3D fractal assemblies, this study demonstrated superior flexibility and energy absorption in tension, torsion, bending, and compression tests, with fracture strains and angles up to 300% and 200% higher than baseline designs. These results highlight their suitability for high-impact applications in aerospace, automotive, robotics, and protective materials. By transitioning from 2D to 3D fractal architectures, this research broadens the potential of metamaterials, offering tunable mechanical properties for a wide range of advanced engineering applications.