Low-velocity impact response of novel hierarchical hexagonal multicell structures

This study introduces two novel hierarchical hexagonal multicell (HHM) tube designs inspired by honeycomb and grass stem structures: full triangular hierarchical hexagonal multicell (FTHHM) and internal clone hierarchical hexagonal multicell (ICHHM). These tubes feature a triangular pattern and hierarchical arrangement with four orders (0 th -3 rd ). The tubes, fabricated from PLA-ST using FDM 3D printing technology, were analyzed through finite element simulations of all hierarchical cross-sectional structures and validated against experimental results. Tubes with higher hierarchical orders consistently reduced total displacement and enhanced crashworthiness performance indices, particularly in crush force efficiency (CFE). Among the designs, the FTHHM-3 tube outperformed the ICHHM-3 tube. Furthermore, the effect of wall thickness on the FTHHM-3 tube was investigated by incrementally increasing the impactor mass until the densification phase was reached across the entire wall thickness. As a result, the FTHHM-3 model exhibited significant improvements in CFE by 24.77% and in specific energy absorption (SEA) by 52.76% compared to conventional hexagonal tubes. These findings indicate that 3D-printed FTHHM tubes, especially those with higher hierarchical orders, hold strong potential for application in future lightweight structural systems.