Self-contacting metamaterials achieving asymmetric, non-reciprocal, and adjustable Poisson’s ratios that break thermodynamic limits

Abstract

Although metamaterials with unconventional Poisson’s ratios have been extensively explored for their counterintuitive and desirable properties, most exhibit only a single behavior. Here, we design novel metamaterials capable of both positive and negative Poisson’s ratios, which simultaneously demonstrate outstanding performances: asymmetric, non-reciprocal, and even exceeding thermodynamic limits. These abnormal properties are achieved by combining honeycomb and re-entrant structures with self-contacting stops set at different positions. The unique topology allows for mode switching, where the unit cell can transition between “honeycomb” and “re-entrant” configurations under different load conditions. This mode convertibility endows the metamaterials not only different signs of Poisson’s ratios under various load conditions in a single direction but also anisotropy in orthogonal directions. Through theoretical analysis, the deformation modes and the corresponding Poisson’s ratios are predicted. Experiments and simulations then validate the intriguing Poisson’s ratios and the model predictions. Notably, these Poisson’s ratios can be further tailored by adjusting the initial states of the self-contacting stops, offering a powerful tool for manipulating Poisson’s ratios and unlocking new functionalities of metamaterials.