The influence of the structural organization of chiral metamaterials on their physical and mechanical characteristics

Metamaterials are artificially created materials which unusual properties are due to their geometric structure, not the chemical composition of the base material. The control of physical and mechanical properties through the structure is fundamental for metamaterials. The tools of the numerical analysis used in this work overweigh experimental tests due to the automation of research, reduced material and financial costs. Here, a tetrachiral metamaterial is investigated under uniaxial compression conditions. The base material is described as an elastic medium. An analysis of the influence of the metamaterial's structural organization on its mechanical response is carried out. To do this, two methods of connecting unit cells are considered: "joining" and "overlapping". The following are selected for the analysis: (1) the tension - torsion coupling effect; (2) effective elastic properties (Poisson's ratio and Young's modulus); (3) porosity; and (4) the state of stress and strain. The porosity of the samples obtained by the "joining" method was 80 % and the "overlapping" method resulted in 84 %, the volume of the base material in the second case was 1.6 times larger. It was found that the tension - torsion coupling effect is affected not only by the volume of the base material but also by the internal organization of the structure, namely, the versatile chirality of the touching faces of the unit cells. Analysis of the numerical experiment results showed that the three - dimensional samples have a zero value for the effective Poisson's ratio. The Young's modulus of the sample in which the cells were connected by the "joining" method turns out to be almost 2.7 times higher. Both samples can be described as an anisotropic medium with a lattice in the cubic system medium, which is shown by studying the properties of metamaterial samples when loaded along three orthogonal axes. The construction created by the "joining" method is characterized by a more heterogeneous pattern of stress distribution and presence of stronger stress concentrators.