Novel dual-platform lightweight metamaterials with auxeticity

Auxetic materials and structures have received extensive attention due to their unusual behavior. As one of the structures that can realize the auxetic effect, the elliptic perforated structure has been recently developed, but the previous research on the elliptic perforated is limited to the small deformation stage. At the end of the small deformation stage, the elliptic perforated structure becomes dense and loses the auxetic effect. The available compression stroke is very short and therefore the structure has relatively lower specific energy absorption (SEA). In order to make better use of material, through the buckling of lightweight perforated plates, a newly designed re-entrant elliptical perforated structure is proposed in this work. The re-entrant cells rotate and move inward (the first stage), and finally be compressed by neighbor ones (the second stage). Therefore, the structure undergoes rotational deformation in stage one same as previous perforated plates but specific re-entrant deformation in the second stage, thereby realizing the auxeticity in large deformation. Experimental and numerical results show that the stress–strain curve exhibits double platforms, and the novel structure possesses the auxetic effect throughout the whole compression process. Subsequently, a parametric analysis of the re-entrant distance and the ratio of horizontal and vertical wall thickness was carried out for obtaining greater auxetic effect and better stability of the novel re-entrant elliptic perforated structure. The material utilization rate of the re-entrant elliptic perforated plate was greatly improved, and the application prospect of the re-entrant elliptic perforated was also discussed.