Synclastic behavior of auxetic metamaterials

Synclastic curvature is consistently mentioned in the literature as one of the unique properties of auxetics, but detailed investigations and comparisons are lacking. The study utilized a bench-top testing device and implemented a series of indicators and evaluation methodologies to examine synclastic curvature behavior. Two tests, namely forming and conformity tests, were conducted on three typical auxetics (reentrant structure (Re), Star lattice (St), and chiral lattice (Ch) as well as two non-auxetic counterparts (Honeycomb structure (Ho) and near zero Poisson's ratio semi-reentrant structure (Se)). These tests aimed to investigate engineering as well as ergonomics applications of the materials. Although auxetics can be formed into a synclastic curvature shape more easily than non-auxetic materials, the low in-plane stiffness that results from this forming process might restrict their applications in the field of engineering. The results of this study indicate that Re is a desirable material for ergonomic applications because of its high conformity to the synclastic curvature surface and a low maximum stress ratio in the contact area. On the other hand, St and Ch demonstrate poor performance in most conditions due to local buckling of the ribs.