The axial crushing performance of bio-inspired hierarchical multi-cell hexagonal tubes

Both the concepts of bio-inspiration and hierarchy are found to be effective in enhancing the crushing perfor-mance of tubes. In this paper, the bio-inspired hierarchical multi-cell hexagonal tubes (BHMH) were developed by combing the bio-mimicked and hierarchical configurations in tubular structures. The crushing behaviors of BHMH tubes with various hierarchical orders and wall thicknesses were firstly investigated numerically. The results show that the peak crushing force (PCF) of all BHMH tubes is less than that of hexagonal tubes in each group, which is beneficial in minimizing possible injury and damage when tubes are crushed. With the increase of hierarchical order and wall thickness, the mean crushing force (MCF), crushing force efficiency (CFE) and specific energy absorption (SEA) of BHMH tubes also increase. The SEA of the third order BHMH tubes is approximately 2.5 times that of the zeroth order BHMH tubes (multi-cell hexagonal tubes) in each of the four groups. Compared with conventional hexagonal tubes, a maximum increase of 146% in the SEA of BHMH tubes is obtained, which demonstrates that BHMH tubes are better energy absorbers than that of traditional single and multi-cell hexagonal tubes. Subsequently, theoretical analysis based on the Simplified Super Folding Element (SSFE) theory was carried out to determine the mean crushing force of BHMH tubes. The theoretical results agree well with the simulated results for all BHMH tubes.