Determination of Poisson’s Ratios of Auxetic Chiral Structures

The transformation of an object from its original shape under the influence of various internal and external forces is called deformation. Auxetic deformation, unlike conventional deformation, can occur irregularly on the object. For this reason, the Poisson’s ratio values of the auxetic materials vary according to the measurement points on the auxetic specimen and different elongation amounts. Although there is no standard experimental method for determining the Poisson’s ratio, which shows the degree of auxeticity in the literature, different methods such as taking measurements from different measurement areas and considering different cell numbers have been used to determine the Poisson’s ratio. However, the calculated Poisson’s ratio represents only the measured points. In this study, the Poisson’s ratios of three different cell structures that are tetra-chiral, antitetra-chiral, and hexa-chiral structures were determined numerically and experimentally at varying elongation amounts of 1mm, 2mm, and 3mm. Auxetic plates with three different chiral structures were produced from PLA material with a three-dimensional printer for experimental analysis. A Digimizer image processing program was used to obtain the Poisson’s ratio in experimental measurements. The specimen was photographed by the device at certain elongations, and the elongation values at the measurement points were obtained through the program. The values of the experimentally established Poisson’s ratio were also calculated numerically using the ANSYS finite element program at varying deformation rates. Thus, the Poisson’s ratios for the changing cell structure, and elongation amount were obtained comparatively and their changes were revealed to establish a measurement standard.