A stretchable sandwich panel metamaterial with auxetic rotating-square surface

Sandwich panels find use as energy-absorbing devices and protective structures in various fields. However, due to their mostly rigid surfaces, they might not meet the protection requirements in complex conditions like non-Euclidean geometries of protected objects. To address this issue, a novel sandwich panel structure inspired by the synclastic curvature behavior of auxetic metamaterial was proposed. The surface of the proposed sandwich panel features rotating squares that allow for horizontal stretching, resulting in an improvement in controllability, auxeticity, flexibility, and synclastic curvature compared to traditional sandwich panels. Experimental and numerical methods were used to compare the similarities and differences between the novel and traditional sandwich panels under uniaxial compression. Additionally, different rotation angles and numbers of unit cells were simulated to examine their mechanical properties. The study also explored the auxeticity, stretchability, synclastic curvature, and potential applications of the novel sandwich panel. It was found that appropriate cuts on the sandwich panel can enhance energy absorption. These findings could pave the way for new opportunities in the application and basic research of sandwich panels while providing ideas for enhancing the survivability of panel structures in complex conditions.