Low-density, high-strength metal mechanical metamaterials beyond the Gibson-Ashby model

Low-density, high-strength, ductile metal mechanical metamaterials are in high demand for engineering applications but remain out of reach by the Gibson-Ashby model. Here, we demonstrate a new design concept based on a generalized theoretical model or an extended Gibson-Ashby model to overcome this challenge. We show that the deformation mechanism of a strut-based metal lattice material depends on its strut length-to-diameter (l/d) ratio, and the key to maximizing its strength is to reduce its l/d ratio to the minimum manufacturable level without increasing the lattice density. Inspired by this design concept, we investigate three strut remodeling strategies to strengthen metal lattices. Our low-density Ti-6Al-4V lattices (1.6 g/cm3) designed according to Wolff's law of bone remodeling achieve exceptional strength (>400 MPa) compared to all cellular metallic materials of equivalent density reported so far (2–8 times their strength). Our l/d-centered design concept is expected to inspire the design of more metal metamaterials.