Production and characterization of the Poisson's ratio of cellular structured metamaterials by additive manufacturing

Metamaterials are materials designed to have peculiar, unconventional electromagnetic, acoustic, thermal, or mechanical properties. These properties do not derive from the chemical composition of the material but rather from its internal structure, characterized by a three-dimensional cellular architecture consisting of a periodic repetition of an elementary cell. Among the properties displayed by metamaterials, the negative Poisson's ratio, also known as auxetic behavior, is the most relevant for what concerns the mechanical behavior, and it results in an increase of the transversal dimension upon tensile elongation. Metamaterials find application in different fields such as biomedical, automotive, aerospace, and textile fields. A big push towards the study of these new materials has certainly been provided by the expansion of additive manufacturing, which allows to easily realize complex geometries without restrictions. The goal of this work is to compare the Poisson's ratio vs strain during tensile tests, carried out on various metamaterials, produced with different structures, with different materials, and by different additive technologies. In particular, chiral, honeycomb and reverse honeycomb geometries have been studied. The structures were produced in PLA and ABS by Material Extrusion and in resin by Stereolithography. The results show that, as expected, the chiral and the reverse honeycomb geometries have a negative Poisson's ratio while the honeycomb geometry has a positive one. Moreover, the samples produced by stereolithography result more ductile with higher deformation at failure. (C) 2022 The Authors. Published by Elsevier B.V.