Fig. 5. Application of bi-beams for designing metamaterials and mechanisms with novel properties and functionalities.

(A) (i) A near-orthogonal unit cell made from predisposed bi-beams was used to form a lattice structure whose Poisson’s ratio is highly dependent on the applied strain rate and could switch between an auxetic (i.e., negative Poisson’s ratio) and a conventional (i.e., a positive Poisson’s ratio) behavior. (ii) Three different sets of material properties were chosen to evaluate the evolution of the Poisson’s ratio with strain under different rates of the applied strain. (iii) Switching from an auxetic to a conventional behavior. Some unit cells from the middle part of the cellular lattice have been magnified for better visualization of the strain distributions. (iv) Experimental observation of strain rate–based switching from an auxetic to a conventional behavior. (B) A circular arrangement of bi-beams was used to transform axial compression to either clockwise or counterclockwise rotation, depending on the applied strain rate. Moreover, the stiffness of the rotational mechanism is highly dependent on the applied strain rate. Photo credit: Shahram Janbaz, Delft University of Technology.