Toucan Beak Citation and Abstract

["Andrew A. Farke" <andyfarke@hotmail.com>]

Following the post from Richard Travsky, the citation and abstract for 

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Seki, Y., M. S. Schneider, and M. A. Meyers. 2005. Structure and mechanical
behavior of a toucan beak. Acta Materialia 53:5281-5296.

The toucan beak, which comprises one third of the length of the bird and yet
only about 1/20th of its mass, has outstanding stiffness. The structure of a
Toco toucan (Ramphastos toco) beak was found to be a sandwich composite with
an exterior of keratin and a fibrous network of closed cells made of
calcium-rich proteins. The keratin layer is comprised of superposed
hexagonal scales (50 [mu]m diameter and 1 [mu]m thickness) glued together.
Its tensile strength is about 50 MPa and Young's modulus is 1.4 GPa. Micro
and nanoindentation hardness measurements corroborate these values. The
keratin shell exhibits a strain-rate sensitivity with a transition from
slippage of the scales due to release of the organic glue, at a low strain
rate (5 x 10-5/s) to fracture of the scales at a higher strain rate (1.5 x
10-3/s). The closed-cell foam is comprised of fibers having a Young's
modulus twice as high as the keratin shells due to their higher calcium
content. The compressive response of the foam was modeled by the
Gibson-Ashby constitutive equations for open and closed-cell foam. There is
a synergistic effect between foam and shell evidenced by experiments and
analysis establishing the separate responses of shell, foam, and foam +
shell. The stability analysis developed by Karam and Gibson, assuming an
idealized circular cross section, was applied to the beak. It shows that the
foam stabilizes the deformation of the beak by providing an elastic
foundation which increases its Brazier and buckling load under flexure
loading.

(abstract available at sciencedirect.com)

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This paper has a bit of relevance for all those who are interested in
modeling dinosaurs and the like--another nice set of material properties to
utilize. A nice little piece of experimental functional morphology.

Andy