Energy absorption characteristics of novel bio-inspired hierarchical anti-tetrachiral structures

Most natural (or biological) materials possess chiral and hierarchical properties, thus can exhibit outstanding mechanical properties, such as shear resistance, vibration attenuation, and impact resistance. Inspired by these natural materials, an innovative category of hierarchical chiral structure is proposed in an attempt to enhance their energy absorption capacity. Based on the chiral element composed of the central ring and connected ligaments, the hierarchical chiral structure is constructed by recursively replacing the central ring with a group of smaller rings connected through ligaments. The energy absorption properties of the present hierarchical structure are numerically analyzed with various hierarchies and impact velocities in terms of the deformation and plastic failure. It is found that hierarchical anti-tetrachiral structures exhibit unique "necking" deformation mode at a low speed impact. In addition, the second-order anti-tetrachiral structures can not only improve the specific mass energy absorption and the specific volume energy absorption but also effectively depress the peak stress compared to the first-order anti-tetrachiral structures. The results provide a new insight into the impact performance of hierarchical chiral and anti-chiral structures, which may contribute to the excellent design of auxetic components for crashworthiness applications.