Mechanical metamaterial with negative Poisson’s ratio based on circular honeycomb core

Mechanical metamaterials are artificial structures with mechanical properties defined by their structure rather than their composition. As a new type of metamaterials with unique mechanical properties and promising prospects, mechanical metamaterials have attracted great attention and become a new hot spot in the field of metamaterials. Mechanical metamaterials with negative Poisson’s ratio can exhibit novel mechanical properties such as excellent resistance capability of bending deformation and indentation. This type of materials have good prospects in many applications such as variant flexible wing skin. In this article, we adopt the design method of mechanical metamaterials to improve the structure of traditional honeycomb core and propose a new type of circular honeycomb core unit to obtain negative Poisson’s ratio. The advantage of circular honeycomb core is that this new structure is more stable than traditional concave hexagon honeycomb core. We established the corresponding mechanical model of this structure and adopted energy method to study the dependencies of structure parameters for its effective elastic modulus. The bending strain energy was taken into consideration while the tension and shear strain energy were ignored because they are very small compared with the bending strain energy. Then the expressions of effective elastic modulus in the directions of X and Y axis can be established in the condition of small deformation. In order to verify the validity of theoretical results, finite-element simulation method was employed to our study and we adopted periodic structure as the finite-element simulation model and aluminium alloy as the base material. The results of theory and the simulation have good agreements, and we found that its effective elastic modulus E_x is mainly depending on its height h and thickness t while E_y is mainly depending on its radius r and thickness t. And the thickness t may bring about deviation between theory and the simulation when it increases. The Poisson’s ratio of this material was also investigated through finite-element simulation method and different values of structure parameters were selected. Among these structure parameters, when h=35 mm, r³21 mm and h=40 mm, r³24 mm or h=45 mm, r³26 mm, negative Poisson’s ratio can be obtained. The results indicate that the composite structure based on circular honeycomb core units can achieve negative Poisson’s ratio, which can be controlled by structure parameters. The excellent mechanical performance of light-weight and its negative Poisson’s ratio make circular honeycomb core a promising candidate as engineering material. And our study may pave a useful path to mechanical metamaterials with negative Poisson’s ratio.