Design of novel 3D auxetic structures based on S-shaped unit-cells

In this study, four novel three-dimensional (3D) warp and woof structures with negative Poisson's ratio (NPR) were designed and assembled using the interlocking assembly method. The designed structures, including S-shaped auxetic unit-cells (UCs), exhibited NPR properties in two perpendicular planes. Because of the lower stress concentration of S-shaped than conventional re-entrant UCs, this UC was suggested for use in energy absorber structures. Furthermore, the mechanical behavior of the designed structures under quasi-static loading was simulated using the finite element method. In addition, two designed structures were fabricated using fused deposition modeling 3D printing technology and subjected to quasi-static compressive loading. The results of FE simulation and experimental work were verified and good agreement was found between them. Stress-strain diagrams, values of energy absorption (W), specific energy absorption (W s), and NPRs in two perpendicular planes were evaluated. The results showed that four designed auxetic structures had NPR in two perpendicular directions. In addition, stress concentration contours of the structures were investigated using FE simulation. Finally, considering the results of energy absorption and stress concentration for designed structures, the proposed structure to be utilized for energy-absorbing systems was introduced.