Biomimicry of the armadillo carapace for the design of bending cylinders for aerospace applications

Shell structures play an important role in aerospace applications and beyond. Various applications require these structures to be able to articulate while maintaining an overall smooth surface to avoid drag. Inspiration for an articulating cylindrical shell is drawn from the hierarchical structure found in the armadillo carapace; this consists of alternating sections of compliant material (collagen fibers) and rigid material (bone tiles). This structure was parameterized to create five separate designs with varied thicknesses of the rigid tiles, while keeping the overall amount of each material constant. This resulted in designs that ranged from spaced, thin vertical rigid rods to continuous horizontal rigid rings – with the volume of compliant and rigid material maintained at 50% each. The designs were modeled with FEM, fabricated using additive manufacturing and tested in tension, compression, and bending. Higher bending stiffness was observed for the vertical rod-shaped designs and the lowest stiffness was obtained for the horizontal ringed design. The ringed design was also the only structure able to reach 20% strain to failure in tension and 10% strain to failure in compression. Digital image correlation revealed that the ringed design also was able to withstand higher local strains during bending than any other design. The ringed design is demonstrated to be a promising option for high strain articulating cylindrical shells. The shape can be further optimized in terms of ring shape, thickness, number of rings, and material options to meet the strains and stiffness values needed for a desired application.