Influence of a novel hierarchical cellular structure on the mechanical behavior: The thousands of eyes bobhi material

The thousands of eyes Bobhis (TEB) is a natural cellular material and has ingeniously evolved hierarchical structures to resist the damage from external environment. In this study, the relationship between cellular structure and mechanical properties of the TEBs is first investigated. SEM studies reveal that the TEB hierarchically exhibit three distinct cellular structures, the filled-cells, novel-closed-cells and open-cells, which is ranging from the macroscopic (>10^-3 m) to the microcosmic scale (10^-4-10^-6 m) respectively. Compression and shear tests indicate that such hierarchical cellular structure has intimate influence on the mechanical properties of TEB. The loads of TEB samples are decomposed through the three hierarchical cellular structures. Microscopically, the multiple micro-cracks are firstly generated from the open-cells, and the novel-closed-cells are deformed and crushed in which the multiple micro shear bands and cell walls interlocking phenomenon can be found in the tests. Macroscopically, the filled-cells are stretched and damaged with the extrusion of filler. The hierarchical cellular structure of TEB possesses excellent mechanical properties, which hinder the catastrophic failure and increase the toughness and strength. The distinct hierarchical cellular structure of TEB provides a new pathway to design bio-inspired engineering materials.