Multi-material 3D double-V metastructures with tailorable Poisson's ratio and thermal expansion

Natural materials have achieved excellent comprehensive mechanical properties and fascinating synergistic functionalities through composite architectures and optimum materials distribution within a single tissue during natural selection/adaptation. Producing three-dimensional (3D) architectures with multi-materials has been a major challenge in artificial materials. Herein, 3D double-V hierarchical (DVH) lattices with multi-materials were designed and fabricated using interlocking assembly strategy. Theoretical analysis, numerical simulation and experimental verification were conducted to investigate the mechanical response of the multi-material metastructures, especially effective Poisson's ratio and coefficient of thermal expansion (CTE). The results revealed that the equivalent Poisson's ratio of the 3D DVH lattices can be tuned by changing not only the geometric parameters but also the relative stiffness of the two V segments. Poisson's ratio of the multi-material metamaterials has the minimum/maximum value at transition point and tends to zero with the increase or decrease of the relative stiffness. The equivalent CTE of concave 3D DVH lattices can be tuned by changing not only the geometric parameters but also the relative CTE and relative stiffness of the two V segments from magnified positive to near zero or large negative. Coupled negative Poisson's ratio and CTE, which are hardly found in natural materials, are easily achieved by the architected DVH composite lattices. This work provides an innovative approach for the design, fabrication and characterization of 3D architected cellular materials with simultaneously tailorable auxetic behavior and thermal expansion, which are promising in advanced engineering applications.