In this study, a new class of three-dimensional (3D) printed metamaterials with auxetic behavior was designed, fabricated, and experimentally analyzed under impact loading conditions. The metamaterials were created by combining multiple unit cells—honeycomb, tetra-chiral, and cubic—in different configurations to enhance their energy absorption capability. All samples were fabricated using the Fused Deposition Modeling (FDM) method with polylactic acid (PLA) material. Impact tests were conducted at three drop heights of 1, 3, and 5 cm to evaluate parameters such as maximum acceleration, absorbed energy, and specific energy absorption. The honeycomb–tetra-chiral–cubic configuration showed the best performance, achieving a specific energy absorption of 5.13 J/g, which was approximately 18% higher than the other designs. The maximum acceleration increased nonlinearly with drop height, indicating a strong dependence on impact energy. A sensitivity analysis performed using Design Expert software demonstrated that impact height was the most influential parameter, followed by Poisson’s ratio and unit-cell type. These findings confirm that combining auxetic geometries in hybrid lattice structures significantly improves energy absorption efficiency, making them promising candidates for use in protective equipment and lightweight structural applications.
Shahmorad et al. (Wed,) studied this question.