Metamaterials with enhanced mechanical properties and tuneable Poisson's ratio

This paper reports a structural modification of an auxetic metamaterial with a combination of representative re-entrant and chiral topologies, namely, a re-entrant chiral auxetic (RCA) metamaterial. The main driving force for the structural modification was to overcome the undesirable properties of the RCA metamaterial such as anisotropic mechanical response under uniaxial compression. Additively manufactured polyamide 12 specimens via Multi Jet Fusion were quasi-statically compressed along the two in-plane directions. The experimental results confirmed that the modified structure was less sensitive to the loading direction and the deformation was more uniform. Moreover, similar energy absorptions were obtained when the modified metamaterial was crushed along the two in-plane directions. The energy absorption per unit volume was improved from 390 to 950 kJ m-3 and from 500 to 1000 kJ m-3 compared with the RCA when they were crushed along the X and Y directions, respectively. The absorbed energy per unit mass (specific energy absorption) also improved from 1.4 to 2.9 J g-1 and from 1.78 to 3.1 J g-1 compared with that of the RCA under the axial compression along the X and Y directions. Furthermore, parametric studies were performed and the effects of geometric parameters of the modified metamaterial were numerically investigated. Tuneable auxetic feature was obtained. The energy absorption and Poisson's ratio of the modified metamaterial offer it a good candidate for a wide range of potential applications in the areas such as aerospace, automotive, and human protective equipment.