A metamaterial with sign-switching and discontinuous Poisson's ratio

The fragmentation-reconstitution (FR) metamaterial has recently been shown to be a suitable candidate for producing Poisson's ratio discontinuity at the original state. A new FR metamaterial is introduced herein that additionally permits sign-switching of Poisson's ratio upon stress reversal along one axis. This was achieved by the use of rotating rhombi in which every rhombus can be further fragmented into six sub-units. The latter consists of two non-rotating smaller rhombi and four rotating isosceles triangles. While results show that the metamaterial exhibits sign-switching of Poisson's ratio upon stress reversal along one axis due to differing mechanism, this is not so for loading in the other on-axis direction due to the dimension being maximum in that direction. Instead, there are two compression pathways which can lead to either fragmentation or reconstitution modes of deformation. The predisposition for each pathway is proposed by means of charge attachments. The uniqueness of this metamaterial avails its use for applications that are not attainable by other materials and metamaterials.