One More New Paper

["Jerry D. Harris" <jharris@dixie.edu>]

Hi Again All -

   One of those papers I have little hope of comprehending fully, since I 
ain't no mathematician nor a physicist, but for the biomechanics in the 
audience:

Seki, Y., M. S. Schneider, and M. A. Meyers. 2005. Structure and mechanical 
behavior of a toucan beak. Acta Materialia 53(20):5281-5296. doi: 
10.1016/j.actamat.2005.04.048.

ABSTRACT: 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 µm diameter and 1 µm 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 × 10^-5/s) to fracture of the scales at a higher 
strain rate (1.5 × 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.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jerry D. Harris
Director of Paleontology
Dixie State College
Science Building
225 South 700 East
St. George, UT  84770   USA
Phone: (435) 652-7758
Fax: (435) 656-4022
E-mail: jharris@dixie.edu
and     dinogami@gmail.com
http://cactus.dixie.edu/jharris/

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