Bending behavior of 3D printed mechanically robust tubular lattice metamaterials

Tubular lattice structures have gained tremendous attention due to their lightweight and excellent mechanical properties. In this work, we designed a new type of tubular lattice architecture by rolling up planar lattice structures with a negative Poisson's ratio, and then fabricated samples using a material jetting 3D printing technique. We investigated their bending behavior under large deformation using a combined experimental and numerical approach. It was found that the proposed auxetic tubular lattice (ATL) structure exhibits a more compliant behavior, and the ductility increased by up to 85.4% compared to that of a conventional diamond tubular lattice (DTL) structure. Meanwhile, the ATL structure is characterized by a local bending behavior due to the auxetic effect, while the DTL structure is featured with global bending mode. Finite element simulations further reveal that the stress on the ATL structure distributes locally around the indenter. In contrast, stress on the DTL structure distributes much more uniformly across the span. As such, the ATL structures exhibit excellent global stability compared to the DTL structure. Our parametric study shows that bending stiffness, maximum load, and ductility of the proposed ATL structure are mainly controlled by beam depth, due to its large exponential contribution to the moment of inertia. Increasing beam depth leads to a more desirable ductility than increasing beam thickness. The beam amplitude and tubular curvature have minor effects on the bending performance compared to other geometric parameters. The findings reported in this work can guide designing and optimizing mechanically robust tubular lattice metamaterials for applications in tissue engineering, biomedical devices, and robotics engineering.