A single input state switching building block harnessing internal instabilities

Mechanical metamaterials are a promising platform to alter mechanical properties post-fabrication. Recent efforts have shown this using a set of external stimuli that control an equivalent set of states, representing material properties, by changing the internal geometry and stresses of a metamaterial unit-cell. To decrease the number of external stimuli for a set of states, a building block is required that uses internal information as an extra input. Here, we present an elastic and contact-less state-changing building block that harnesses internal instabilities to switch between two distinct states as a response to a single stimulus. The building block consists of a buckling beam at its bifurcation, a nonlinear spring and a bistable element representing the internal information state. Upon applying a stimulus in the form of a displacement, the state is measured by the nonlinear spring which determines the desired deformation branch of the buckling beam at bifurcation; as a result the internal state will switch to the other stable state. Such a state-changing building block can be associated with geometric changes in the cellular structure, resulting in different material properties.