Rapid control of multimodal mechanical metamaterial collapse using pneumatic pressurization

Pneumatically pressurized mechanical metamaterials have been shown to achieve large deformation and programmable mechanical properties using networks of enclosed cavities. Yet, many applications of pneumatic pressurization are limited by a moderate rate of actuation. Here, a bimodal, dual-stage mechanical metamaterial is presented that achieves rapid switching between collapse modes using pneumatic pressurization and elastic instabilities. The two collapse modes are described using kinematic models where deformation occurs only as ligament bending. Each mode experiences two stages of collapse resulting in fully compact configurations. The collapse modes can be programmed passively with the relative sizes of ligaments and actively through pneumatic pressure to selected cavities. The mechanical properties of a multimodal metamaterial sample under biaxial compression are shown with a gradation of applied pressures. By applying or removing pressure during collapse, the metamaterial will rapidly switch from one collapse mode to the other. This demonstrates an integrated ability to tune the mechanical properties of the metamaterial in real-time.