A novel 3D-printed unit cell with the compression-torsion coupling effect and negative Poisson's ratio

Metamaterials have received extensive research interests since they can be artificially designed to achieve unprecedent material properties beyond what we can obtain from the nature. As such, it is widely acknowledged that metamaterials have great potential application perspectives in many areas, e.g., mechanical engineering, civil engineering, aerospace, biomedical engineering, etc. Recently, mechanical metamaterials that are designed based on multi-functional properties or behaviours have received much attention due to the increasing demands of new materials with superior properties. Inspired by the grasshopper's leg, this paper proposes a novel unit cell where 3D 'zig-zag' rods are introduced to connect the circular planar elements. The mechanical behaviours of this novel unit cell under axial compression are studied both experimentally and numerically. In particular, the effect of different geometric parameters of the 3D 'zig-zag' rod on both compression-torsion coupling (CTC) and negative Poisson's ratio (NPR) are studied for this novel unit cell. Compared with previous designs, the novel unit cell proposed in this work can improve the design flexibility, achieve large NPR, strong CTC, and high loadcarrying capacity, simultaneously. Finally, this work can provide some references for designing novel metamaterials with multiple deformation mechanisms.