Nanomechanical properties and the hierarchical structure of elytra cuticle of dung beetle (Copris ochus Motschulsky)

Natural biomaterials are complex composites in hierarchical structure and multifunction. They have some special structures and functions because of their evolution through the exchanges of energy, matter and information with their surroundings over millions of years. The cuticle represents 25% of the dry weight of the entire insect body. It is tenacity, waterproof and lightweight which is an excellent crude composite material. An increasing interest in bionic design of materials based on structures of natural biomaterials has led to the nanomechanical characterization of biomaterials. Quantitive measurement of mechanical properties of insect cuticle will help to develop biomimetic materials suitable for industrial products. Field emission scanning electron microscopy (FESEM) was used to investigate the detail structure of elytra cross section in transverse direction and longitudinal direction. Shown in transverse direction, the fibers of the deeper layers of the endocuticle are orientated in rotation angle and neighbor fibers are rotated in relation to the each other in the same direction. While the fibers in longitudinal direction show the epicuticle, exocuticle and endocuticle clearly hierarchically structure in parallel. In this work, the mechanical properties of the elytra cuticle of dung beetle Copris ochus Motschulsky, reduced modulus and hardness in nano-scale, were investigated by using a nanoindenter. The reduced modulus (E_v) and hardness (H_v) of surface cuticle in the vertical direction obtained by nanoindentation was 5.96 ? 0.32 GPa and 0.32 ? 0.09 GPa, respectively. The nanoindentation result was shown that the reduced modulus (E_t, E₁) and hardness (H_t, H₁) of each layer was gradually reduced from the outer layer to the inner layer in the transverse direction and the longitudinal direction, respectively. E_v was less than the largest E_t presented at outer layer (7.34 ?- - 0.27 GPa) and was larger than that of E₁(6.05 ? 1.12 GPa) which shows the anisotropy of chitin fibers. It was supposedly formed as a result of the composite effect of the hierarchically structure.