Geometric Analysis and Experimental Studies of Hexachiral Structures

Chiral metamaterial structures exhibit auxetic properties—when subjected to stress, they either contract or expand in the given direction, while maintaining an asymmetric geometric effect—they cannot overlap with their mirror image. The unit cells of hexachiral structures take the form of cylindrical nodes with ligaments attached to them. Under the action of external compressive forces, the ligaments bend and coil around the nodes. This is accompanied by a negative Poisson’s ratio approaching minus one. In this case, it has been demonstrated both theoretically and experimentally that this value is independent of the degree of compression. In the course of geometric analysis, the value of Poisson’s ratio has been shown to depend on the number of unit cells in the structure, and with a large number of unit cells, it reaches the theoretical value of minus one. The experiments were conducted on structures assembled from printed nodes and ligaments. It has been demonstrated that, as a result of uniaxial compression, various parts of the structure undergo distinct deformations. However, structures subjected to multi-directional compression—as elastic energy reservoirs—also exhibited negative Poisson’s ratio values close to minus one, with their magnitude dependent on the degree of compression.