Creating a Three-Dimensional Auxetic System Using Torsion Springs

In this article, a three-dimensional (3D) auxetic system is designed by linking layers of rotating squares with torsion springs. The orientation of the rotating squares in the different layers is organized in such a way that when a tensile load is applied on them, corresponding squares would rotate in opposite directions. This creates a torque that acts on the torsion spring. As a consequence, the length of the torsion spring increases resulting in a negative Poisson's ratio in three dimensions. An analytical model for the Poisson's ratio is derived and then tested using a 3D-printed specimen of the proposed design. The results are found to be in general good agreement.