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

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.