Geometrically tunable architected materials designed from prismatic rotating units

An exotic property of some mechanical metamaterials is their negative Poisson's ratio which is of interest for many applications, from biomedical to aeronautic. This work investigates how a mechanical metamaterial evolved from equilateral triangular rotating prisms changes its Poisson's ratio according to the orientation of the reference units with respect to the tensile loading direction (aligned or 45° rotated, respectively). Different configurations are investigated through kinematic analysis, which describes hinged couplings in the linked vertices of the prisms. The best configurations emerging from the kinematic analysis were converted into chiral architectures: Three-dimensional printed physical prototypes were tested under uniaxial compression and the results compared with finite element predictions. The experimental results showed a remarkably different deformation behaviour between the metamaterial designs, with a good qualitative agreement with the numerical simulations. High values of auxetic response are observed for the configuration whose cells are aligned with the load, while a low auxetic and less sensitive geometry variation behaviour was observed for the rotated cell architecture. This rotated configuration also exhibits the significant achievement of mechanical properties which are approximately independent of the geometry variations.