The mechanical properties and the topological structure of cross-sections found in Cybister elytra are presented.SEM images show the similar geometric structure in transverse and longitudinal sections.Elytra consist of several layers:a dense,black epicuticle,an exocuticle that is braided by several parallel chitin fiber layers in a helix structure,and many bridge piers formed by the fiber bundles that connect the exocuticle to the endodermis,forming a composite,light-weight biomaterial.The mechanical properties along the edge of elytra are measured using a nano-indenter.The hardness and modulus of fresh cybister elytra is 0.31 GPa and 6.13 GPa,respectively.The ultimate stresses of fresh elytra,measured by using a tensile test machine,are 169.2 MPa and 194.5 MPa in the transverse and longitudinal directions,respectively,which is twice higher than that of the dried one.The difference in the two directions indicates that this bio-material has been topologically optimized during evolution.The results may provide a biological template to inspire lightweight structure design for aerospace engineering.
