A new three-dimensional re-entrant negative Poisson's ratio metamaterial with tunable stiffness

Re-entrant structure, as a branch of mechanical metamaterial, has attracted attention due to its excellent mechanical properties. However, this structure suffers from the defect that the initial stiffness and load capacity are not customizable, which limits its practical application in engineering. Therefore, it is important to study a new type of three-dimensional re-entrant negative Poisson's ratio (NPR) structure that can tailor mechanical features like stiffness, load capacity, and energy absorption, and is suitable for practical engineering applications. In this work, a re-entrant unit with different sizes of γ (re-entrant column clearance) was designed, manufactured, and tested to achieve the adjustability a function of original stiffness and capacity for load by adjusting the size of γ. The accuracy between the finite element results and the actual results was verified through experiments and numerical analysis. In addition, the mechanical properties of the new re-entrant structure were compared with those of the conventional re-entrant structure. Using the verified finite element model, the influence of different structural parameter ratios on the initial stiffness, load capacity, energy absorption, and Poisson's ratio of the new re-entrant structure was analyzed. The results show that different sizes of γ can change the structure's mechanical attributes, realizing the adjustability of mechanical properties and providing a new method for the study of mechanical properties of NPR metamaterial.