Mechanical properties of a hybrid auxetic metamaterial and metastructure system

We propose in this work an innovative hybrid auxetic metamaterial with a centresymmetric unit cell and tessellation topology similar to the one provided by the missing ribs configuration. The tessellation proposed is applied to different core unit cells (star shape, cross-chiral shape with same dimensions and re-entrant). The effects of the geometric parameters of the cells on the in-plane mechanical properties of this hybrid auxetic metamaterial system are investigated via finite elements (FEM). Representative unit cells (RUCs) with optimal mechanical behaviors are identified; those configurations exhibit the larger negative Poisson's ratios and enhanced specific moduli. Designs related to two groups of auxetic metastructures with cylindric and cubic shapes are then developed based on the optimized RUCs along x and y directions. The equivalent mechanical performance of these metastructures under internal pressure is evaluated from a numerical standpoint. Auxetic cylindrical metastructures can be tailored by adjusting the number of the optimized RUCs along the circumferential and longitudinal directions, together with the geometric parameters of the optimized RUC itself. These hybrid auxetic metamaterials and metastructures provide the potential for multifunctional applications in biomechanics, flexible electronics and aerospace.