Enhancing the energy absorption capability of auxetic metamaterials through auxetic cells within re-entrant circular units

Re-entrant circular (REC) auxetic metamaterials have garnered significant attention in structural engineering due to their enhanced energy absorption capability and reduced stress concentration compared to traditional re-entrant auxetic configurations. However, there is considerable potential for further enhancing their design to achieve even greater energy absorption capabilities. This study introduces three novel REC auxetic structures (REC-S, REC-Star and REC-Flower) specifically designed to enhance energy absorption capabilities compared to traditional REC configurations. These structures are formed by deploying an S-shaped, a star, and a newly designed auxetic unit-cell (UC) named Flower into the REC framework and fabricated through 3D printing by using fused deposition modeling (FDM) techniques. Their deformation behavior and mechanical performance are assessed through quasi-static compressive experimental tests and finite element analysis (FEA), with good agreement obtained between the two sets of results. Based on the validated FEA, the effects of the geometrical parameters of the structures on specific stiffness (E_s), specific energy absorption (SEA), and Poisson's ratio are further investigated. The results show that the newly designed structures outperform the traditional REC structure with equivalent relative densities (∆ρ) and the REC-Flower has the highest SEA for all relative densities, positioning it as a promising candidate for the next generation of REC structures.