A study on the structure and mechanical behavior of the Dasypus novemcinctus shell

Multiscale hierarchical structures, materials properties, and mechanical behaviors of the nine-banded armadillo (Dasypus novemcinctus) shell were studied to provide fundamental knowledge for understanding biological composite systems. The nine-banded armadillo's dermal shell is characterized into three regions: the forward, band, and rear shells. The forward and rear shells comprise a sandwich composite structure of functionally graded material having relatively denser exterior bony layers and an interior bony network of foam. The forward and rear shell's strength (~ 1500 MPa) was greater than the intermediate band shell (~ 500 MPa). The band shell revealed a more complicated structure where adjacent bands are partially overlapped and connected with each other to provide flexibility, in addition to protection. Hardness tests showed that the top surfaces of each shell had hardness (~ Hv50) greater than the front and side surfaces (~ Hv40). Compression test results on the forward and rear shells showed a typical nonlinear deformation behavior similar to synthetic foams, where microbuckling is a key inelastic deformation mechanism. A comparison and contrasting study of the structure-property relations between the armadillo shell and other biological structural materials could provide fundamental understandings for deformation mechanisms that can lead to the development of novel bio-inspired safety system design methodologies.