Thermally Programmable Multi-stable Mechanical Metamaterial

Abstract

Until recently, multi-stable mechanical metamaterials have been primarily used in passive energy absorption systems. However, the ability to actively program these structures has gained significant interest, expanding their functionality to enable on-demand adaptive deformation. While existing active programming methods effectively induce global state transitions, localized actuation remains largely unexplored. This study introduces a novel approach to actively programming multi-stable metamaterials via local thermal stiffness modulation at boundary conditions. Using a polymer bi-material design with distinct glass transition temperatures between the beam and boundary supports, the system can transition from a bi-stable to a mono-stable state, enabling controlled snap-back behaviour after deformation. An analytical model is developed to characterize the snap-through behaviour of the unit cell, providing insight into the geometric interactions and sensitivities associated with various design parameters. Experimental implementation, using multiple additive manufacturing techniques, revealed key limitations and design considerations. In particular, the importance of constraining the second buckling mode and careful material selection emerged as fundamental design requirements for ensuring functionality. This work contributes to the growing field of actively programmable mechanical metamaterials, with implications for compact motion systems in future work.