Mechanical metamaterials enable unconventional and programmable mechanical responses through structural design rather than material composition. In this work, we introduce a multistable mechanical metamaterial that exhibits a toggleable stiffness effect, where the effective shear stiffness switches discretely between stable configurations. The mechanical analysis of surrogate beam models of the unit cell reveal that this behavior originates from the rotation transmitted by the support beams to the curved beam, which governs the balance between bending and axial deformation. The stiffness ratio between the two states of the unit cell can be tuned by varying the slenderness of the support beams or by incorporating localized hinges that modulate rotational transfer. Experiments on 3D-printed prototypes validate the numerical predictions, confirming consistent stiffness toggling across different geometries. Finally, we demonstrate a monolithic soft clutch that leverages this effect to achieve programmable, stepwise stiffness modulation. This work establishes a design strategy for toggleable stiffness using multistable metamaterials, paving the way for adaptive, lightweight, and autonomous systems in soft robotics and smart structures.

翻译：机械超材料通过结构设计而非材料成分实现了非常规且可编程的机械响应。在本研究中，我们提出了一种多稳态机械超材料，其展现出可切换的刚度效应：有效剪切刚度在不同稳定构型之间发生离散式切换。通过对单胞替代梁模型的力学分析发现，该行为源于支撑梁传递至曲梁的旋转，该旋转主导了弯曲变形与轴向变形之间的平衡。单胞两种状态之间的刚度比可通过调整支撑梁的细长比或引入调节旋转传递的局部铰链进行调控。对3D打印样品的实验验证了数值预测，证实了在不同几何构型下均存在一致的刚度切换现象。最后，我们展示了一种利用此效应实现可编程、阶梯式刚度调节的整体式软离合器。本研究确立了利用多稳态超材料实现可切换刚度的设计策略，为软体机器人与智能结构中的自适应、轻量化和自主系统开辟了新途径。