A 2D auxetikos system based on interconnected shurikens

Abstract

A 2D material that expands biaxially upon thermal change, regardless of whether the temperature increases or decreases, is introduced herein. To do so, it must possess an overall conventional or positive thermal expansion under the influence of heating, but the coefficient of thermal expansion must switch to a negative value upon cooling. A novel microstructure is proposed herein in the form of interconnected shuriken network, whereby each rigid shuriken is connected to four connecting rods via four pairs of rotating rods. All rods contract during cooling but the swiveling of the rotating rod produces a net increase of the unit cell expansion in spite of the connecting rod contraction, thereby leading to an overall negative thermal expansion. During heating, the rotating rods are made redundant through the action of an interlocking mechanism while the connecting rods expand, thereby resulting in an overall positive thermal expansion. The capability for the material system to flip the sign of its thermal expansivity paves a way for engineers to design material systems that possess opposing properties in order to respond in a consistent manner in spite of opposing stimuli.