title: Armadillo armor: mechanical testing and micro-structural evaluation.
abstract: The armadillo has a unique protective bony armor, called the osteoderm, which confers to its shell-like skin distinctive mechanical properties. The top layer of the shell is made out of a dark-brown keratin layer with bimodal size scales. Beneath the keratin layer, the osteoderm consists of hexagonal or triangular tiles having a composition that is the same as bone. The tiles are connected by non-mineralized collagen fibers, called Sharpey's fibers. The tough and highly mineralized tiles have a tensile strength of approximately 20 MPa and toughness of around 1.1 MJ/m3. In comparison, the hydrated osteoderm has a lower tensile strength of ∼16 MPa and a toughness of 0.5 MJ/m3. The tensile failure occurs by the stretching and rupture of the Sharpey's fibers. In a specially designed punch test in which an individual tile is pushed out, the shear strength is ∼18 MPa, close to the tensile strength of the osteoderm. This surprising result is interpreted in terms of deformation in the Sharpey's fibers in the hydrated condition. The armadillo shell and a turtle shell are compared, with their corresponding similarities and differences.
authors.affiliation: Materials Science and Engineering Program, Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Irene H
authors.initials: IH
authors.lastname: Chen
authors.forename: James H
authors.initials: JH
authors.lastname: Kiang
authors.forename: Victor
authors.initials: V
authors.lastname: Correa
authors.forename: Maria I
authors.initials: MI
authors.lastname: Lopez
authors.forename: Po-Yu
authors.initials: PY
authors.lastname: Chen
authors.forename: Joanna
authors.initials: J
authors.lastname: McKittrick
authors.forename: Marc A
authors.initials: MA
authors.lastname: Meyers
mesh_terms: D000818:Animals; D001135:Armadillos / Q000033:anatomy & histology*; D006253:Haversian System / Q000033:anatomy & histology; D008422:Materials Testing; D055595:Mechanical Phenomena; D011235:Predatory Behavior; D012867:Skin / Q000033:anatomy & histology; D013314:Stress, Mechanical