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Morphology, nano-mechanical properties and bending fracture stress of hind leg material of Cybister japonicus beetle

Biomaterials are complex composites with hierarchical structure and multi-function. The mechanical properties of biomaterials are often outstanding, especially considering their weak constituents. After evolving for millions of years to adapt to water surroundings, the diving beetles Cybister japonicus possess a pair of relatively large flattened hind legs which are optimized for sliding and rowing functions for swimming. In this paper, the morphology and microstructures of the hind leg biomaterial of Cybister japonicus are observed by scanning electron microscope (SEM). The nano-mechanical properties of the hind leg cuticle are measured with a nano-indentation system and the bending fracture stress is investigated by employing a multi-functional mechanical properties testing machine. The results of this study provide an appropriate biological pattern for the structural design of novel advanced lightweight composites with high specific strength.