The mechanical implementations in three kinds of color-changing beetle elytra

With superior adaptability, some elytron as modified forewing can perform mechanical protection for underlying hindwing and soft body while conduct color-changing in dynamically natural environment. There are mainly three color-changing styles of angle dependence, irreversible and reversible color-changing for elytra. Here, Popillia indgigonacea Motsch, Sagra femorata purpurea Lichtenstein and Dynastes tityus were chosen to investigate the relationship between color formation of three color-changing styles and mechanical properties of light weight and high strength. The optical and nanomechanical properties of purplish red S. f. p. Lichtenstein were obtained through angle-resolved spectroscopy system and nanoindenter, respectively. In finite element analysis, three geometrical structure models of color-changing relevant, irrelevant and the whole elytron models were designed, and then mechanical properties of six coupled bionic models of each beetle were investigated. The multilayer, convex closures and photonic crystal in the epicuticle can complete the dynamic presentation of structural colors by interference, scattering and photonic band gap when resourcefully resist external forces in low/high stress and strain with high/small elastic modulus and hardness. Meanwhile, other microstructures of multilayer and trabecular hollow are reasonably constructed to cooperatively display mechanical properties of light weight and high strength.