Mechanics of a Tunable Bistable Metamaterial with Shape Memory Polymer

Bistable metamaterials, characterized by their ability to transition between two stable configurations, find applications in the fields of morphing structures, energy harvesting systems, and bionics. Shape memory polymers (SMP) are a class of smart materials that can revert to their original shape from a deformed state when subjected to appropriate stimuli. In this study, we have designed and manufactured a tunable bistable metamaterial incorporating SMP, utilizing 3D printing technology. The unit cell of the metamaterial comprises a curved beam supported by walls. By modifying the material distribution, the structure can transition from a monostable to bistable states. To deepen our understanding of the underlying mechanisms of the tunable bistable metamaterial, we developed a theoretical model that quantifies the characteristics of state transitions. In particular, our theory can accurately predict the criteria for state transitions, governed by the modulus ratio between the curved beam and supporting walls. The accuracy of these criteria is validated through a combination of experimental and theoretical analyses, alongside finite element simulations. By applying this criterion, we can readily control the material's modulus ratio in the structure through thermal stimuli, thereby demonstrating the feasibility of tunable and programmable bistable metamaterials in this work.