Investigation to nano corkscrew structure in Lucanidae cuticle

The microstructure of a Lucanidae cuticle was observed with a scanning electronic microscope (SEM). It was found that the insect cuticle is a kind of biocomposite consisting of nanometer chitin fibers and sclerotic-protein matrix. There is a kind of corkscrew nano-chitin-fiber structure in the cuticle, in which the fibers in different layers have different orientations, which may improve the fracture toughness of the cuticle. The maximum pullout force of the corkscrew nano-chitin-fiber structure was analyzed and compared with that of the conventional parallel-fiber structure based on their representative volume element. It showed that the maximum pullout force of the corkscrew nano-chitin-fiber structure is markedly larger than that of the conventional parallel-fiber structure. A comparative experiment on the maximum pullout forces of the corkscrew-fiber and the parallel-fiber structures was conducted. Comparison shows that the analytical results agree well with the experimental results.