Negative mechanical materials and metamaterials : giant out-of-plane auxeticity from multi-dimensional wine-rack-like motifs

Abstract

‘Negative mechanical materials / metamaterials’ refer to materials and/or engineered systems that exhibit anomalous macroscopic thermo-mechanical properties that emerge due to the structure of their subunits, rather than the specific chemical composition. As a result of their design/construction, they may exhibit anomalous macroscopic properties such as zero or negative Poisson’s ratios (auxetic), moduli and/or indices. Such zero/negative properties are not normally manifested by their conventional counterparts and may thus potentially be used in applications where typical materials cannot. This work will look into some of the more recent developments made in this field, focusing on how existing materials (e.g. crystals) are providing the blueprint for the design and manufacture of novel’ negative materials’. In particular, this work looks at how wine-rack like crystalline materials which are typically studied for their negative thermal expansion and/or negative compressibility properties can be modified so as to generate negative Poisson’s ratio through a novel mechanism involving forcing elements to move out-of-plane to generate giant out-of-plane auxeticity.