Mechanical Metamaterials with Discontinuous and Tension/Compression‐Dependent Positive/Negative Poisson's Ratio

Ordinary materials have positive Poisson's ratios (PRs), and the currently known mechanical metamaterials possess negative PRs both under tension and compression. Herein, two types of novel cellular structure units with tension/compression‐dependent positive/negative PRs are demonstrated. For type I structure, the unit exhibits a positive PR during tension and a negative PR during compression, while for type II structure, the unit shows a negative PR during tension and a positive PR during compression. The deformation behaviors of the new metamaterials are first predicted by a simple analytical model and finite‐element method calculations, and the predicted results are then confirmed experimentally. Numerical and experimental studies show that for the plane angle α