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ARO Exoskeleton Materials


This work investigates the multiscaled structure and the constitutive behavior of the exoskeleton of arthropods (Japanese beetle) along with the response of biomimicked structures. Image analysis (SEM and TEM) revealed three load-bearing regions comprised of chitin-protein fiber layers orientated parallel to the cuticle surface. The chitin fibers in the exocuticle and mesocuticle are organized in a helicoidal structure (layers stacked with a small rotational angle relative to their adjacent layers). The endocuticle has a distinct pseudo-orthogonal pattern, characterized by a thin transitional helicoidal region inserted between two orthogonal layers. Idealized mechanics based models showed that the pseudo-orthogonal structure redistributes the stresses, and reduces the maximum tensile stress and transverse shear stress in the cross-section, thus making the structure able to tolerate larger external loads. Furthermore, the interfacial strain energy release rate is lower in the pseudo-orthogonal structure compared to the cross-ply laminate, suggesting that the pseudo-orthogonal structure may be more resistant to fracture. The bio-inspired laminated composite structures, designed and manufactured, showed improved mechanical properties over the conventional industry standard structure, primarily the residual strength under static load. In all, these observations may be used to produce durable man-made materials and structures.


Final Report ARO W911NF-08-1-0493