Heterostructured mechanical metamaterials inspired by the shell of Strombus gigas

Despite being highly mineralized, the shells of molluscs exhibit superior strength and toughness because their architectural designs control the evolution of cracks and other types of localized deformation such as shear bands. The crossed-lamellar design of the shell of Strombus gigas, whose hierarchy consists of four distinct lamellar-shaped features assembled in a three-dimensional arrangement, represents the toughest of all seashells. A mechanical metamaterial that adapts the geometrical design of this queen conch is anticipated to circumvent the typical trade-offs between strength-ductility and strength-density. Inspired by the three-dimensional hierarchical and interactive architecture of the crossed-lamellar microstructure, we instruct the design of bio-inspired metamaterials that mitigate failure from the extension of a single shear band and instead develop numerous smaller bands confined within the individual plank-like zones introduced in their layered geometric design. The measured strength properties of these materials are found to increase in inverse proportion to the square root of the thickness of the layers in the hierarchy as a result of progressive deformation enabled by cross-layer interactions. The results provide a new perspective on the design of strong and tough mechanical metamaterials.