Predictions of Young's modulus and negative Poisson's ratio of auxetic foams

Auxetic foams possess negative Poisson's ratio, exhibiting unique mechanical properties. A modified model based on the quasi-three-dimensional model of Choi and Lakes is developed for auxetic foams and the formula of the volumetric compression ratio is also corrected in this study. Three deformation mechanisms of all cell ribs (i.e. stretching, shearing and bending) are incorporated. By applying the newly modified model, the theoretical results of Young's modulus and Poisson's ratio depend on the folded angle of the bent ribs, the relative density, the shape of the rib cross section and the Young's modulus and Poisson's ratio of the virgin material. The predicted values of the effective Young's modulus and Poisson's ratio of auxetic foams compare favourably with experimental data. In addition, a finite element analysis model is proposed to predict the value of Poisson's ratio in this study. The two models can be reduced to predict the mechanical properties of conventional foams, and exhibit the process of the conversion of conventional foams into auxetic foams. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim