Angle‐Dependent Transitions Between Structural Bistability and Multistability

Abstract

Mechanical metamaterials with multi‐nonpositive indexes, especially for a negative Poisson's ratio (NPR)/zero Poisson's ratio (ZPR), negative stiffness (NS)/zero stiffness (ZS), and negative thermal expansion (NTE)/zero thermal expansion (ZTE), have garnered significant interest due to their unprecedented mechanical properties and functional applications for advanced materials and devices. Architected materials with one abnormal index, such as auxetic materials, have been widely studied based on mature and diverse underlying mechanisms. However, metastructures with double or multiple abnormal indexes are rarely reported due to the possible coupling effects between the indexes. Herein, triple‐negative‐index (NPR, NS, and NTE) structural bistability is achieved using assembled composite materials with hexagonal auxetic frameworks and compressed buckled bistable snapping segments. Double‐negative‐one‐zero‐index (NS, NTE, and ZPR) or double‐zero‐one‐negative‐index (ZPR, ZTE, and NS) structural multistability is achieved using assembled composites with rectangular frameworks and compressed buckled bistable snapping segments. Particularly, angle‐dependent transitions between robust structural bistability and multistability are achieved with controllable isotropic or anisotropic thermal expansion. This study demonstrates rationally designed metastructures with multiple abnormal indexes and the potential applications of multifunctional metamaterials.