Programming mechanical metamaterial properties with boundary displacement constraint

Mechanical metamaterials typically achieve programmable mechanical behavior through geometric design or responsive materials. However, these strategies often suffer from limited tunability after fabrication and constrained functional versatility. In this study, we introduce the boundary displacement constraint (BDC) to actively program mechanical responses by imposing controlled displacements at the system's boundaries. Using the rotating block architecture as a model system, we experimentally demonstrate that varying levels of boundary precompression can modulate structural stiffness, alter stress-strain responses, and enhance impact resilience. We derive an energy-based theoretical framework that accurately predicts stiffness variations across different constraint conditions. Finite element simulations confirm that stiffness modulation primarily arises from constraint-induced suppression of block rotations. Under dynamic impact, BDC effectively governs internal structural deformation, resulting in tunable and enhanced mechanical performance. The metamaterials with BDC allow rapid, precise, and reversible tuning of mechanical properties without internal redesign or relying on smart materials, offering a powerful new paradigm for adaptive mechanical systems.