Micro-tensile Testing of the Lightweight Laminated Structures of Beetle Elytra Cuticle

Quantitative measurements of the mechanical properties of insect cuticle are a useful tool in the development of bio-mimetic materials suitable for industrial products. In this study, a micro-tensile tester was used to investigate the mechanical properties of elytra cuticle of the dung beetle (Copris ochus Motschulsky). Micro tensile testing show that: yield strength (Fs) =17.12±3.55N, Maximum tensile (Fb) =14.74±4.11N, yield strength ( ) =1.4±0.15GPa, tensile strength ( )=1.2±0.21GPa, elastic modulus(E) =14.56±4.20GPa, plastic index(δ) =0.241±0.10. Tensile elongation of the specimens was between 12.1-36.3%. Our results demonstrate that the elytra possess ductile material characteristics. Field emission scanning electron microscopy (FESEM) was used to investigate the detailed structure of the elytra cross section in both the transverse and longitudinal directions. In the transverse direction, the fibers of the deeper layers of the endocuticle are orientated in a constant, rotated angle with neighboring fibers rotated in relation to the each other in the same direction. The fibers in the longitudinal direction show that the epicuticle, exocuticle and endocuticle layers clearly create a parallel hierarchical structure. We believe this is a result of the composite effect of the hierarchical structure. Finally, we developed a laminated model based on the parameters provided by tensile testing, FESEM imaging and nanoindentation measurements, and compared the results of the model to our experimental results. Key words: nanoindentation; micro-tensile testing; coupled analysis; laminated structure