Buckling elastomeric springs and lattices for tailored energy absorption

Mechanical metamaterials exploiting elastic instabilities offer energy absorbing performance that exceeds the limits of conventional foams. Here, we thoroughly investigate the energy absorption of buckling elastomeric springs made by additive manufacturing (AM), which we refer to as chi (χ) springs because of their shape. We designed and fabricated 518 elastomer spring parts to thoroughly explore the parameters space by systematically varying L, θ, the S, and O, utilizing the ability of AM to quickly and precisely tailor the geometry. We conducted quasi-static compression tests and extracted the energy absorption properties, including the plateau stress σ_p and width w_p, the absorbed energy W, and energy absorption efficiency η. Owing to their unique chiral buckling morphology, the springs have superior energy absorption exceeding ideal stochastic open-cell foam even with a single unit cell. The springs achieve η of 21.2 – 53.3%, while achieving a wide range of σ_p from 4.6 kPa to 149.0 kPa. Using commercially available AM elastomeric polyurethane, the springs bridge the property space region between conventional open-cell and closed-cell foams in terms of W and σ_p. We show concepts for tessellating the spring into periodic lattice structures. Overall, the effective properties and the ability to readily produce these springs and lattices with AM enable multifunctional parts with integrated energy absorption for use in helmets and protective packaging.