Date of Graduation

12-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Civil Engineering

Advisor

Panneer R. Selvam

Committee Member

Kevin D. Hall

Second Committee Member

John F. Peters

Third Committee Member

Ernie Heymsfield

Fourth Committee Member

Min Zou

Keywords

Pure sciences; Biological sciences; Applied sciences; Bio-engineered composites; Biochemistry; Biomechanics; Biomineralized composites; Exoskeleton fish scale; Hard and soft interfaces

Abstract

The U.S. Army has determined a huge cost savings of up to 51% can be accomplished by reducing the gross vehicle weight, for their personnel carrier, by 33%. To cut cost, composite materials are needed. Man-made composites can have superior material properties (high-strength, high-fracture toughness, and lightweight), but they are prone to delamination at the glued-layered interface. In contrast, fish scale is a natural composite that has the same material properties and, additionally, tend not to delaminate.

The focus of this study was to learn how nature integrates hard and soft materials at each length scale to form a layered composite that better resists delamination. Previous research conducted by others had suggested that from the nano-to-millimeter length scale the individual components of the fish scale are glued to form layers in the composite. My research provided a detailed description, using novel experiments, to explain how hard and soft materials have been mixed/integrated at each length scale, optimized by volume fractions, and subtly vary material properties. The material variations were compared to mechanical properties of modulus, hardness, and for the first time energy dissipation.

(a) The combination of the hard (inorganic minerals) and soft (polymer-like organic collagen fibers) are integrated instead of being glued at the nano scale. At the micron scale for the two-layered composite the outer dental enamel (hard) layered interface uses a saw tooth shaped joint to connect to the inner bone (hard open-like foam) layer. At the millimeter scale the material and mechanical properties are gradually graded through the thickness, away from the interface.

(b) Within each layer, at the micron scale, there are subtle variations in materials. However, the outer dental enamel (hard) layer has 90-percent hard (inorganic minerals), 10 percent (polymer-like organic collagen fibers), by volume. Whereas, the inner bone (hard open-like foam) layer has 60 percent hard (inorganic minerals) and 40 percent (polymer-like organic collagen fibers), by volume.

(c) Because hard and soft materials are mixed/integrated within the layers from the nano-to-micro length scales; along with property away from the interface at the millimeter scale the local stresses that lead to delamination are reduced.

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