Investigation on Effects of Geometric Parameters on the Negative Poisson’s Ratio of a Reentrant Structure

Abstract

It is not common to find negative Poisson’s ratio in nature but it exists in auxetic materials. The auxetic property enables the material to elongate in both vertical and horizontal directions under tension. Cellular honeycombs with repetitive reentrant cells are a common example of auxetics. This thesis investigates the geometric impacts of a reentrant structure originating from honeycombs on the negative Poisson’s ratio of the structure. Finite Element Method is used for the simulation, with the commercial software ANSYS APDL 15.0. The negative Poisson’s ratios under different geometric parameters are discussed based on the simulation results with small displacement and linear plane elements. Geometric non-linearity is also taken into consideration for large displacement which occurs in the experiments. Non-linear plane elements are used in the simulation with non-linear geometric deformations. Experimental Poisson’s ratios are collected from tension tests conducted on 3D printed reentrant honeycomb structures, to evaluate the simulation’s accuracy. The simulated results do reflect the same trend in the geometric effects on the negative Poisson’s ratio compared to the corresponding experimental cases, although, there are numerical discrepancies between simulation and experiments. Causes of the differences are analysed. Possible improvements which can be carried out in the future are suggested.