Lattice structures (LSs) are increasingly celebrated for their lightweight characteristics and superior mechanical performance. In this research, a strut reinforcement technique was employed to enhance the energy absorption capacities of 3D re-entrant auxetic (Aux), hexagonal (Hex), and hybrid auxetic-hexagonal (AuxHex) lattice structures. The investigation involved finite element analysis (FEA) to delve into the mechanical and energy absorption properties of these novel designs during quasi-static compression testing. To accurately simulate the mechanical behavior of the 3D-printed lattice structures, the mechanical properties of the PA2200 matrix material-manufactured via 3D printing-were utilized. The results from the uniaxial loading tests of the reinforced designs were then compared with those from traditional 3D hexagonal and re-entrant auxetic lattice structures. The elastic modulus of the reinforced designs was improved by 130% for hexagonal structure, 85.78% for auxetic structure, and 168.26% for hybrid auxetic-hexagonal structure at a 2 mm strut diameter. Similarly, the reinforced designs showed a significant increase in volumetric energy absorption (W). Reinforced Hex structure had a 153% improvement in W, whereas reinforced Aux and AuxHex structures showed an increase in W by 162.4% and 119.09%, respectively. Comparing energy absorption properties of all structures at the same relative density, the W of the reinforced hexagonal structure was found to be the highest. The experimental validation of the compression responses of the 3D-printed lattice structures demonstrated good agreement in terms of elastic modulus, yield stress, peak stress, and deformation modes. Finally, the deformation patterns of the reinforced auxetic and hexagonal structures were identified to be a combination of bending and stretching dominating, resulting in increased stiffness, load-bearing capacity, and weight efficiency.
