Thermomechanically Triggered Reversible Multi-Transformability Of A Single Material System By Energy Swapping And Shape Memory Effects

Thermally triggered active metamaterials with shape memory polymers (SMPs) show greater potential for structural applications with reconfigurability than other programmable structures owing to their temporally stiff condition with shape locking. However, most SMP-based active metamaterials have not shown complex transformation, such as multi-modal and asymmetric deformations, because of the lack of an adaptable strategy with reasonable mechanics models. Moreover, conventional SMP has a critical drawback - irreversible transformability, limiting its reconfigurability for active metamaterials. Herein, a thermomechanical tool that allows a single material system to transform with reversible, multi-modal, and asymmetric deformations is constructed and demonstrated. Using transformation aids (TAs), a localized pre-stress and a temperature-dependent reverse stiffness effect to exchange energy with a lattice is conceived. The deformation of a single SMP system whose energy is swapped from TAs by localized pre-stress and reverse stiffness can transform into reversible, multi-modal, and asymmetric deformations with shape-locking. The methods can be used for reconfigurable structures, tuning symmetry, and chirality, especially for active acoustic metamaterials, deployable devices, and biomedical devices. The mechanics-inspired design approach of local deformation of TA and the interaction with the temperature-dependent stiffness drop of the lattice open an avenue to the robust design of thermally triggered active metamaterials.