Nanoindentation investigation of the stress exponent for the creep of dung beetle (Copris ochus Motschulsky) cuticle.

ABSTACT With the rapid development of bionic science, especially the progress that has been made in the fields of biomaterials and biomimetics, there is now great interest in the surface and internal mechanical properties of biological materials at the micro- and nanoscale. The study of micro- and nanoscale biomaterial mechanical properties could enable interdisciplinary applications in materials science, biological science and bionic science. Dung beetle (Copris ochus Motschulsky) cuticle is a viscoelastic material that is both viscous and flexible via elastic deformation under external forces; where stress σ, strain ϵ and elastic modulus E are related in the following way: σ = Eϵ. In addition, as σ is related to the rate of strain, time is also a factor. The stress-strain relationships of various parts of dung beetle cuticle were investigated in this paper. As time increased, the stress and strain of the material were found to decrease and increase, respectively, indicating that when the material was indented for a certain period, the interaction force between the indenter and the material gradually achieved a state of dynamic equilibrium. However, strain continued to occur until reaching a point of equilibrium because of the creep phenomenon. The stress-strain curves showed a strong character in each holding time condition: the longer the holding time, the more flattened the stress-strain curve. These findings will be useful in the advanced design of strong, lightweight, and biomimetic composites.