Modified re-entrant auxetic metamaterials with energy absorption enhancement

The re-entrant auxetic topology was one of the first unit-cells proposed to build cellular auxetic structures. This unit cell (UC) is still widely used in energy-absorbing systems, but there is considerable scope for enhancing its design. This paper describes a series of experimental tests and finite element (FE) models used to evaluate the energy absorption capabilities of novel auxetic structures based on replacing straight struts of the re-entrant unit cell with curved-shaped ones. Three structures have been first designed and manufactured using fused deposition modeling (FDM) 3D printing techniques. The samples have then been subjected to quasi-static compressive testing. The results have been compared with those of a traditional re-entrant structure having similar relative densities and showed that the modified metamaterial topologies demonstrate significantly improved energy absorption and specific energy absorption (SEA) capabilities. In addition, all the proposed new topologies exhibit negative Poisson's ratio (NPR). After selecting the structure with the highest SEA, a geometrical parametric analysis has been performed to investigate the design space to enhance overall SEA and NPR values. The proposed work provides an overview of the state-of-the-art in re-entrant auxetic structures and introduces a new class of modified re-entrant metamaterials with remarkable energy absorption capability.