Three-dimensional auxetic metamaterials with extremely tunable flexible behavior

Abstract

Flexible auxetic metamaterials has demonstrated significant potential in engineering applications. However, most existing flexible auxetic metamaterials are limited to two-dimensional (2D) designs, restricting their utility in real 3D engineering scenarios. Here we represent a versatile strategy for designing 3D auxetic metamaterials that showcase extraordinary flexibility, recoverability, and programmability which is accomplished by embedding truss lattice with elastic spring into rotating rigid frameworks. We exemplify this approach with the eccentric spring connected rotating octet truss structures (ROCT-S) through experimental, numerical, and theoretical analysis. Under in-plane tension, engineering stress of the proposed eccentric spring connected rotating octet truss structures in two directions (ROCT-S-2D) is approximately 9.4 × 10⁻⁶ of the base material's modulus at an average strain of 161 %. Simultaneously, the programmable mechanical performance of the ROCT-S-2D under out-plane compression is decoupling with their in-plane performance and can be designed to support a load exceeding 12,800 times its own weight. The robust and adaptable mechanical performance of ROCT-S highlight its broad applicability, spanning electronics and biomedical devices to wearable flexible protective gear, paving the way for advanced 3D auxetic metamaterials in practical engineering solutions.