The Twisting of Dome-Like Metamaterial from Brittle to Ductile

Abstract

Architected materials can exhibit mechanical properties that do not occur with ordinary solids. By integrating hierarchy and size effects, microarchitected metamaterials fabricated by two-photon lithography with a metallic or ceramic coating can be ultrastrong but lightweight. However, the attainment of both strength and ductility is generally mutually exclusive. Inspired by the Pantheon dome in Rome, which can withstand high load while keeping low density, microarchitected domes with a gradient helix are designed and deposited in a hierarchical nanostructured aluminum film with ultrahigh strength and considerable plasticity. Despite having a thick coating, which usually causes catastrophic collapse, the thick-walled metallic dome shows recoverability during compression. The compressive strength increases to 73 times that of current ductile-like microlattices, leading to the metamaterial occupying the domain of the material property space that is hitherto empty. Detailed in situ experimental and computational work reveals the graceful (noncatastrophic) failure due to the helical twisting and plastic flow in the supra-nanomaterial. It is a promising method of suppressing brittle failure via a combination of architectural and material design. It can be used to impart enhanced functionality, making programmable stiffness, and tailored energy absorption all possible.