On simultaneous positive and negative Poisson's ratio laminates

Studies on the mechanical behavior of materials are often performed on the assumption of positive Poisson's ratio except for auxetic materials. Auxetic materials and structures are intriguing systems that exhibit negative Poisson's ratio. Recently some investigation were made on semi-auxetic materials in terms of their directional and positional auxeticity. In this paper we furnish a simple example of a 3-ply laminate consisting of isotropic plies whereby the sign of its effective Poisson's ratio changes when the loading mode changes between pure axial loading and pure bending. In addition, both positive and negative Poisson ratio behaviors do not cancel one another, but are simultaneously manifested when the above-mentioned loading modes are combined. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.