Rolling contact bistable passive and active metamaterials

Abstract

Negative stiffness and bistability are desirable properties to improve the speed and power of actuators, dissipate energy in shock absorbers, and provide stable switching mechanisms. However, most negative stiffness mechanisms cannot deliver large strain capacity, high force density and long fatigue life simultaneously due to plastic strain accumulation. We propose a new class of metamaterial featuring rolling flexible beam deformation that enables control over strain responses in architected materials. In addition, multiple rolling beams can be incorporated in a unit cell to significantly amplify the force density and metamaterials with rolling beams can be used as passive flexible structures or bistable actuators. The elastic properties of these metamaterials are examined through tensile tests and finite element analysis. Negligible changes in the force-displacement response are observed after more than 10,000 cycles. The performance of electroactive rolling versions are evaluated using dielectrophoretic liquid zipping actuation, demonstrating power amplification through snapping. Moreover, the rolling mechanism enables this bistable design to facilitate both linear and rotational motions, or a combination of both. This is demonstrated in applications including an efficient perching mechanism for drones and rapid-response grippers, illustrating the wide potential impact of this rolling contact metamaterial mechanism.