Variable stiffness is a key capability in biological and robotic systems, enabling adaptive interaction across tasks and environments. Mechanical metamaterials offer an alternative to conventional mechatronic solutions by encoding stiffness variation directly into monolithic structural architectures, reducing the need for discrete assemblies. Here, we introduce a multistable mechanical metamaterial that exhibits a toggleable stiffness effect in which the effective shear stiffness switches discretely between stable mechanical configurations. Mechanical analysis of surrogate beam models of the unit cell reveals that this behavior originates from the rotation transmitted by the support beams to the curved beam, governing the balance between bending and axial deformation. Consequently, the shear stiffness ratio between the two states 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 and confirm 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, with potential applications in soft robotics and smart structures where adaptive compliance is of paramount importance.

翻译：变刚度是生物与机器人系统中的关键能力，实现了跨任务与环境的自适应交互。机械超材料为传统机电一体化方案提供了替代路径，通过将刚度变化直接编码到整体结构架构中，减少了离散组件的需求。本文提出一种具有可切换刚度效应的多稳态机械超材料，其有效剪切刚度可在稳定力学构型之间离散切换。对单胞替代梁模型的力学分析表明，该行为源于支撑梁传递至曲梁的旋转运动，从而调控弯曲变形与轴向变形之间的平衡。两种状态间的剪切刚度比可通过改变支撑梁的长细比或引入调节旋转传递的局部铰链进行调谐。基于3D打印原型的实验验证了数值预测结果，并确认不同几何构型下均能实现一致的刚度切换。最后，我们展示了一种利用该效应实现可编程阶梯式刚度调节的整体式软离合器。本研究建立了基于多稳态超材料的可切换刚度设计策略，在自适应柔顺性至关重要的软体机器人与智能结构中具有潜在应用前景。