Strain‐Activated Mechanical Metamaterial With Programmable Dual‐Phase Stiffness and Enhanced Energy Absorption

ABSTRACT

Mechanical metamaterials enable programmable responses that can transcend conventional material behavior. Here, we introduce a metamaterial architecture that exhibits an intrinsic dual‐phase elastic response through a geometrically programmed deformation pathway. Our proposed auxetic‐inspired unit cell incorporates internal locking arms that activate sequentially under compression and induce a smooth transition from a bending‐dominated to a stretching‐dominated deformation regime. This mechanism yields two distinct and stable states of elastic modulus. It enables tunable stiffness and enhanced energy dissipation within a single architecture. A systematic design framework that combines finite‐element simulations and design‐of‐experiments revealed the key geometrical parameters that govern phase‐transitioning behavior. Additively manufactured prototypes confirm the predicted dual‐phase response under compression, demonstrating strong agreement with simulations. Additively manufactured and FE‐simulated 4 × 4 lattice structures confirmed the usability of the proposed design. This work establishes a pathway for mechanically programmable metamaterials that integrate controlled stiffness transition and optimized energy absorption that would open opportunities for adaptive protective systems, soft robotics, and morphing structures.