Design and manufacture of 3D auxetic structures for tunable mechanical properties

Auxetic metamaterials are promising for various engineering applications; however, their performance is often compromised by inherent auxeticity and high porosity. Recently, the 3D folded structure (3D FS) has demonstrated potential for multi-stage energy absorption. Therefore, herein, we propose four novel auxetic structures (AUX-1 to AUX-4) by systematically modifying the wall orientation of the 3D FS to achieve tunable and enhanced mechanical properties. The proposed structures were designed, additively manufactured, and experimentally tested under quasi-static compression. Finite element (FE) simulations were also conducted to elucidate deformation mechanisms and establish structure-property relationships. The mechanical and energy absorption performance of the structures was evaluated and compared with that of the 3D FS. All the structures exhibit double plateau stress and negative Poisson’s ratio (NPR) characteristics. Notably, the AUX-2 structure achieves a 16% improvement in crushing force efficiency (CFE) in the first plateau region, which is attributed to a more homogeneous stress distribution. It also exhibits a maximum NPR increase of 6% at the beginning of loading. The AUX-4 structure exhibits a 412.5% increase in energy absorption capacity within the first plateau region, despite a 30% reduction in CFE due to stress fluctuations. The incorporation of horizontal and vertical walls in AUX-1 and AUX-4 enhances the elastic properties while lowering the NPR. The AUX-3 structure demonstrates improvements in elastic properties and energy absorption performance. However, it exhibits a slight decrease in CFE in the first plateau region and a slight decrease in NPR throughout the deformation.