  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.
