A bio-inspired auxetic metamaterial with two plateau regimes: Compressive properties and energy absorption

Auxetics are a unique class of materials that exhibit a negative Poisson's ratio (NPR) owing to their distinguish deformation behavior. However, some auxetics are either weak in their in-plane directions and/or deform non-uniformly under quasi-static compression, resulting in inferior mechanical performance. This study aims to develop an auxetic metamaterial with relatively uniform deformation pattern and superior energy absorption capability. Inspired by the geometry of a butterfly, a novel auxetic metamaterial, namely, butterfly-shaped auxetic metamaterial (BSAM), was developed. The in-plane compressive performances of the proposed metamaterial were experimentally and numerically investigated. Polyamide11 specimens were 3D printed using Multi Jet Fusion (MJF). NPRs were observed during the compression along both directions. The compressed BSAM revealed two distinctive plateau regimes in its nominal stress-strain curves. Influences of specific parameters on the mechanical performance and energy absorption of the BSAM were numerically examined. Moreover, when BSAM was compressed along the Y direction, the specific energy absorption outperformed that of BSAM compressed along the X direction. A comparative study was carried out using the validated numerical models between the proposed metamaterial (BSAM) and two other popular auxetic honeycombs: re-entrant and anti-tetrachiral. Young's moduli and plateau stresses of the BSAM were significantly surpasses those of the two honeycombs. Moreover, the specific energy absorption per unit mass (SEA) were 2.4 and 3.2 times that of re-entrant honeycomb when they were compressed along the X and Y directions, respectively. Meanwhile, the SEA of the BSAM in the X and Y directions were 2.1 and 2.7 times that of the anti-tetrachiral honeycomb. The exquisite geometric configurations of the BSAM revealed distinguished and controllable mechanical properties which could sheds light on the possibility to design bio-inspired metamaterial with multi plateau regimes and energy absorption capacities for specific applications.