Multistable mechanical metamaterials with compatible sensitive actuation and high stability

Multistable mechanical metamaterials (MMMs) program shape reconfigurations through snap-through transitions between multiple stable states in response to environmental stimuli, such as changes in mechanical load, temperature, or magnetic field. One major unresolved challenge is the trade-off resulting from the inherent coupling between the critical actuation load and the multistability. MMMs that require high actuation loads to snap through exhibit strong mechanical stability but are difficult to trigger and cannot respond to small-amplitude environmental stimuli. In contrast, those that can snap through under low loads become highly susceptible to disturbances and may fail to maintain multistability. This study introduces a tri-beam bistable building block to decouple critical actuation load and structural multistability. The constructed MMMs are capable of programming strain energy barriers into their layouts to achieve multistability under arbitrary actuation loads, even low to near-zero. The mechanical properties and deformation mechanisms of MMMs are investigated via a combination of numerical simulation, analytical modeling, and experimental validation. The proposed heterogeneous discrete assembly strategy integrates rigid and flexible components into MMM unit cells, enabling support-free additive manufacturing of reconfigurable one-directional, planar, and spatial MMMs with near-isotropic mechanical behavior. The developed MMMs exhibit post-manufacturing re-programmable deformation, high compactability, and multi-directional stability.