Manufacturable curved links as a route to reduce the Poisson’s ratio of auxetic lattice metamaterials

This study demonstrates improved auxetic behavior through the use of curved links in ordered metamaterials. This new approach was shown to reduce the Poisson’s ratio by 0.2 across the whole elastic range, when compared to existing linear re-entrant auxetic structures. The design approach stemmed from observations of curved link auxetic behavior in crumpled structures. This indicated that the edge length per unit volume was dominant in reducing the Poisson’s ratio, rather than the re-entrant angle, as often claimed in the literature. To leverage this approach, curved link functions were integrated into re-entrant structures. A set of smooth functions were then assessed using the finite element method, and validated with a series of physical tests on 3D printed auxetic lattices. Increasing the edge length per unit volume from 7.8 m −2 to 8.8 m −2 was found to reduce the Poisson’s ratio by up to 0.3. The potential uses are broad; the 70% increase in the magnitude of the Poisson’s ratio strengthened material deformation and leads to improved capabilities within strain based design, with substantial potential for light weight impact bearing structures in sports, transport and medical applications.