A novel mechanical metamaterial with tunable stiffness and individually adjustable poisson's ratio

In this study, a novel mechanical metamaterial with sign-switchable Poisson's ratio and tunable stiffness is proposed. Unlike conventional materials with unchanged positive or negative Poisson's ratios under the different loading direction, this novel metamaterial features a negative Poisson's ratio in tension and a positive Poisson's ratio in compression. Due to the nonlinear effect caused by self-contact under compression, this novel metamaterial exhibits obvious tension-compression stiffness asymmetry, and the stiffness varies largely under compression. Parametric studies reveal that the Poisson's ratio and stiffness variation characteristics can be greatly adjusted in one loading direction, but the characteristics in the other direction have little influence. The 2D unit cell is further extended to 3D cylindrical metamaterials, which also maintain these unique characteristics. The proposed structure can be applied to self-locking structures, fasteners, mechanical sensors, and guide the design of multifunctional metamaterials.