Twin Mechanical Metamaterials.

By mimicking the geometrical relation of nano-twin crystals, we propose novel architected twin mechanical metamaterials (TMMs), which can impede local shearing band formation under external loading, thus avoiding global catastrophic failure. The effects of twin-space and twin angle on the mechanical performance of TMMs were also explored, such as: energy absorption, strength, and crack propagation resistance. The results showed that the twin topology design can not only significantly improve the energy-absorption efficiency but also remarkably improve the crack-propagation resistances of stretching-dominant mechanical metamaterials. We also studied the effect of twin-space and twin angle on the tensile strength of TMMs. This study is the first to report on the inverse Hall-Petch effect of TMMs. Our findings open an avenue for the design and fabrication of advanced materials with exceptionally tuneable mechanical properties.