<p>Owing to natural evolution, biological materials and systems have possessed unique capabilities to withstand impact loadings resulting from defense and combat, providing an incredible source of inspiration for designing novel energy absorbers in engineering applications. Hierarchical structures with elaborate architectures have always been potential candidates for exceptional energy absorbers. Bamboo-inspired tubular honeycomb has been a hot topic recently. However, available results are based on partial morphologies extracted from the cross-section of the bamboo with limited implication. A more generalized and fundamental analysis of the hierarchical and gradient nature of the microstructure in bamboo is visioned to provide profound insights to understand new mechanisms in structure design for energy absorption. Herein, inspired by the hierarchical microstructures of the bamboo culm wall, we propose a tubular honeycomb with a structural hierarchy where thin-walled tubes are connected by connection plates and arranged at the vertex of the hexagon in each hierarchical order. To comprehensively understand the energy absorption performances of the bamboo-inspired tubular honeycomb, we employ various energy absorption indicators in accordance with the load-displacement curves, including specific energy absorption (SEA), mean crushing force (MCF), and crushing force efficiency (CFE). Subsequently, we demonstrate the outstanding energy absorption capabilities through experiments and numerical simulations. In contrast to the traditional honeycomb, all the tubular honeycombs possess superior and efficient energy absorption performances owing to the vertex-based circular tubes. Also, the energy absorption capacity is increasing as the hierarchical order. A theoretical model is developed and demonstrated to capture the fundamental characteristics of the structural hierarchy in tubular honeycombs, and the energy absorption capacity of tubular honeycombs with different hierarchical orders is accurately predicted. Furthermore, as an effective strategy to improve the energy absorption performances of cellular materials, the density-gradient design is adopted and coupled with structural hierarchy by assigning a distinct thickness on hierarchical orders of bamboo-inspired tubular honeycombs. We explore the coupling effect of structural hierarchy and functional gradient, where two distinct gradient directions (i.e., the positive and negative configurations) are analyzed, where the positive configuration was demonstrated to achieve enhanced energy absorption capacity, yet the negative gradient is weakening the enhanced effect of structural hierarchy on energy absorption capacity. Given the positive gradient configuration, the mechanism map is theoretically developed to evaluate the integrated effect of geometric parameters, structural hierarchy, and gradient on energy absorption performances of tubular honeycombs and, in turn, guide the next generation energy absorbers design. Compared to conventional cellular materials and other bio-inspired structures, the proposed tubular honeycombs with structural hierarchy and functional gradient exhibit superior energy absorption performances with a large tuning range. &nbsp;</p>

Energy Absorption Performances of Bamboo-Inspired Tubular Honeycomb With Structural Hierarchy and Functional Gradient

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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