Equivalent theories and tension properties of semi-reentrant structures

Abstract

Semi Reentrant structures, which exhibit zero Poisson’s ratio and monoclastic curvature, are combinations of hexagonal Honeycomb and auxetic Reentrant structures. Deflections and strain analysis based on the deformation of unit cells were conducted, and four different equivalent theories for predicting the elastic modulus and Poison’s ratio in two in-plane directions were developed by considering different mechanisms, including flexural, stretching, hinging and shearing deformations, as well as the influence of cell wall thickness. Single sidewall and double sidewall were considered for the cell wall thickness. The theoretical models of Semi Reentrant structures cell could be obtained by assuming that the deformation is a combination of deformation for a hexagonal honeycomb cell (with a positive angle) and a Reentrant cell (with a negative angle). The effectiveness and accuracy of the four theoretical models for Semi Reentrant structures were validated by comparing with the corresponding tensile test simulation results via the finite element method. It was indicated that the fourth theories (T4) were the most accurate, which include the consideration of flexural, stretching, hinging, shearing deformations and cell wall thickness. The influence of geometrical parameters (inclined arm length l, vertical arm length h, angle α, angle β, structure thickness d and cell wall thickness t) on the in-plane tensile properties (elastic modulus and stiffness) was also analysed in tensile test simulations via the finite element method. Comparison of tension results between Semi Reentrant, Reentrant and Honeycomb demonstrated that the mechanical properties of Semi Reentrant were combinations between the others.