Mechanics of a tunable bistable metamaterial with shape memory polymer

Abstract Bistable metamaterials, characterized by the ability of transition between two stable configurations, are applied in fields of morphing structures, energy harvesting system and bionics. Shape memory polymers (SMP) are a class of smart materials which can recover to its original shape from deformed shapes with appropriate stimuli. In this study, a tunable bistable metamaterial with SMP is designed and manufactured utilizing 3D printing technology. The unit cell of the metamaterial consists of a curved beam and the supporting walls. By modifying the material distribution, the structure can transfer from a monostable state to bistable states. To gain deeper understanding in the underlying mechanisms of the tunable bistable metamaterial, we developed a theoretical model to quantify the characteristics of state transitions. Especially, our theory can precisely predict the criteria of state transitions, which is governed by the modulus ratio of curved beam and supporting walls. The accuracy of the criteria was validated through a combination of experimental and theoretical analyses, as well as finite element simulations. Utilizing such a criterion, we can easily control the modulus ratio of materials in the structure by applying thermal stimuli, and the feasibility of tunable and programable bistable metamaterials are further demonstrated in this work.