Effect of design parameters on auxetic behavior and stiffness of additively manufactured 316L stainless steel

Abstract

Auxetic structures, characterized by showing negative Poisson's ratio (ʋ) when loaded, are cellular metamaterials consisting of connected struts in repeating unit cells. The mechanical behavior of auxetics depends on dimensions of the unit cell such as height and length of the unit cell, strut thickness (St), and orientation angle (θ) of the struts. The present study investigates effects of variations in St and θ on ʋ and stiffness (E) of additively manufactured 316L stainless steel with re-entrant honeycomb auxetics fabricated by laser powder bed fusion technique. Poisson's ratio was acquired through linear elastic simulations via finite element analysis (FEA) and verified experimentally through digital image correlation (DIC) facility attached to tensile tests. The design of the auxetic patterns entailed a simulation of thirty-five distinct models, incorporating St values of 0.4–1.6 mm, as well as θ values of 70–90°. In comparison, experimental validation was conducted on nine specimens, featuring St values of 0.6–1.4 mm, and θ values of 70–80°. FEA and experimental results obtained by DIC exhibited ʋ values of −5.23 to −0.3 (for St 0.6-1.4 mm and θ 70–80°), displaying increased ʋ with reductions in both St and/or θ. Meanwhile, E increased with St increase or θ decrease, exhibiting values of 18.9–72 GPa, which could be optimized to fit with human bones stiffness as potential orthopedics implantation in future.

Keywords

• Negative Poisson's ratio
• Laser powder bed fusion
• Finite element analysis
• Digital image correlation
• Strut thickness
• Re-entrant orientation angle