Electronic Theses and Dissertations

Date of Award


Document Type


Degree Name

M.S. in Engineering Science


Mechanical Engineering

First Advisor

Arunachalam M. Rajendran

Second Advisor

Tyrus McCarty

Third Advisor

P. Raju Mantena

Relational Format



The Alligator gar possesses a flexible dermal armor consisting of overlapping ganoid scales. Each scale is a bilayer hydroxyapatite and collagen-based bio-laminate for protection against predation. The exoskeleton fish scale is comprised of a stiff outer ganoine layer, a characteristic "sawtooth" pattern at the interface and a compliant bone inner layer with all materials exhibiting a decreasing elastic modulus, yield strength and density through the thickness. Experiments on ganoid scales revealed properties such as damage mitigation and energy dissipation that are unique to biological dermal armor. The objective of this investigation is to develop a fundamental understanding of the stress response of a fish scale under tensile and shear loading conditions and to compute effective elastic properties. The effects of material grading and the influence of the geometrically and materially nonlinear interface between the ganoine and bone layers on the elastic properties were also considered. A three dimensional finite element method (FEM) was used by employing ABAQUS® code. The current work also investigated possible mechanisms associated with delamination resistance and energy dissipation of the bio-laminate structures. The model structure for the fish scale in the FEM was Alligator gar. The finite element analysis (FEA) is based on a microscopic representative volume element (RVE) of the fish scale with an overall thickness of 800 micron. The FEA RVE had one million uniform 8-micron cubical 8-node elements. The geometrically nonlinear sawtooth features are explicitly modeled. An elastic-plastic model described the nonlinear material response. The analysis focused on evaluating the nonlinear material response in terms of energy dissipation and stress redistribution at the ganoine-bone interface. The results indicate that a complex redistribution of stresses across the 800 micron thickness occurred due to functional gradation of properties, from the stiff mineralized ganoine to the soft bone layer. While the stress concentration was limited to the interface between the saw tooth and the surrounding bone layer, the average stresses in the ganoine layer were much lower as compared to the distributions in the bone layer. The internal energy at the ganoine-bone interface is reduced and energy is dissipated across the sawtooth junction points.



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.