Design and mechanical characteristics of auxetic metamaterial with tunable stiffness

Auxetic materials are a class of mechanical metamaterials. They exhibit lateral expansion under tension, and lateral contraction under compression. Such metamaterials have attracted increasing attention due to their unusual mechanical behavior and various potential applications. However, the stiffness of auxetic structures is much weaker than that of solid ones due to their porous structure. Therefore, many researchers try to enhance the stiffness of auxetic cellular structures to broaden their potential applications. In this study, re-entrant unit cells with different variable stiffness factors (VSF) were designed to achieve the tunability of stiffness from the aspect of tuning the densification strain. Experimental and numerical analyses were carried out to verify the accuracy between the designed and the actual VSF. It is found that the compaction points of the proposed re-entrant structures could be tuned quantitatively using the defined VSF, which provides a new method for the optimal design of negative Poisson's ratio unit cell.