Pre-Torsion Tubular Metamaterials: Multi-Effect Integration for Advanced Functional Applications.

Mechanical metamaterials continuously push the boundaries of mechanical properties far beyond conventional materials. However, a critical step toward the applications of metamaterials lies in combining multiple effects and functionalities into a single structure. Here, a pre-torsion design paradigm is proposed to enable synergistic coupling of distinct mechanical properties. By incorporating such a paradigm into the auxetic tubular structures (ATSs), the robust and superior multi-effect integration (MEI) performance consisting of compression-torsion and auxetic effect under both axial compression and tension is achieved, and the underlying mechanisms are investigated numerically and experimentally. To further demonstrate their benefits in practical engineering, pre-torsion auxetic nails are fabricated based on this design philosophy. Driving-in tests have confirmed their MEI property and manifested extraordinary easy-insertion and damage-free performance. Compared to conventional nails, the pre-torsion nail demonstrates a 52% reduction in energy consumption during wood penetration, along with a 27.1% decrease in initial peak force. This work bridges a crucial gap toward the applications of mechanical metamaterials and can be extended to various engineering scenarios for the design of functional structures and devices.