Design, fabrication, and characterization of solid–liquid dual-state mechanical metamaterials

High-performance and reusable energy-absorbing materials have tremendous potential in industrial applications. Achieving both high performance and reusability has long been a challenge due to their apparent incompatibility. To address this, we proposed a solid–liquid dual-state mechanical metamaterial. This metamaterial exhibits robust mechanical properties when the liquid metal is solid and achieves high energy absorption through its plastic deformation. Upon heating-induced solid–liquid state transition, its deformed state fully recovers its initial state, ensuring reusability. The metamaterials can be fabricated by injecting liquid metal into an hollow elastic lattice structure manufactured through additive manufacturing processes. The mechanical properties of solid–liquid dual-state mechanical metamaterials prepared from different liquid metal, such as gallium, Field's metal, and Wood's metal, are analyzed in this paper through a combined approach of experiments, theoretical analysis, and numerical simulations. The results reveal that the proposed metamaterial significantly outperforms all previously reported reusable energy-absorbing materials in specific energy absorption (SEA). This breakthrough driven by the solid–liquid state transition redefines the limits of reusable energy absorption and opens the path to develop a complete family of robust, reusable materials.