Bistable auxetics

A building block of an auxetic metamaterial, the building block comprising:

• a rotating element centrally disposed within the building block and having three or more vertex points, the rotating element being rotatable about a center of rotation between a first stable state and a second stable state, the rotating element maintaining a fixed orientation in each one of the first and second stable states in absence of load imposed on the building block;
• three or more translating elements disposed around the rotating element and pivotally connected thereto by hinges, each one of the translating elements being pivotally connected to one of the vertex points of the rotating element by a corresponding hinge to permit relative rotation between the translating elements and the rotating element;
• and
• the building block being deformable between a collapsed position and an expanded position, wherein the rotating element is disposed in the first stable state in said collapsed position and in the second stable state in the expanded position, and translation of the translating elements in respective opposed directions away from the center of rotation of the rotating element causes rotation of the rotating element from the first stable state to the second stable state, and translation of the translating elements in respective opposed directions toward the center of rotation of the rotating element causes rotation of the rotating element from the second stable state to the first stable state.

A unit cell of an auxetic metamaterial, the unit cell comprising:

• a plurality of building blocks, each building block comprising:
• a rotating element centrally disposed within the building block and having three or more vertex points, the rotating element being rotatable about a center of rotation between a first stable state and a second stable state, the rotating element maintaining a fixed orientation in each one of the first and second stable states in absence of load imposed on the building block;
• three or more of translating elements disposed around the rotating element and pivotally connected thereto by hinges, each one of the translating elements being pivotally connected to one of the vertex points of the rotating element by a corresponding hinge to permit relative rotation between the translating elements and the rotating element;
• and
• the building block being deformable between a collapsed position and an expanded position, wherein the rotating element is disposed in the first stable state in said collapsed position and in the second stable state in the expanded position, and translation of the translating elements in respective opposed directions away from the center of rotation of the rotating element causes rotation of the rotating element from the first stable state to the second stable state, and translation of the translating elements in respective opposed directions toward the center of rotation of the rotating element causes rotation of the rotating element from the second stable state to the first stable state;
• wherein two adjacent building blocks are at least connected to each other by connecting a first translating element of a first building block to a second translating element of a second building block.