Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Horstemeyer, Mark F.

Committee Member

Rhee, Hongjoo

Committee Member

McKittrick, Joanna

Committee Member

Liao, Jun

Committee Member

Williams, Lakiesha

Date of Degree

8-6-2011

Document Type

Dissertation - Open Access

Major

Mechanical Engineering.

Degree Name

Doctor of Philosophy

College

James Worth Bagley College of Engineering

Department

Department of Mechanical Engineering

Abstract

A recently emerging engineering design approach entails studying the brilliant design solutions found in nature with an aim to develop design strategies that mimic the remarkable efficiency found in biological systems. This novel engineering approach is referred to as bio-inspired design. In this context, the present study quantifies the structure-property relations in bighorn sheep (Ovis canadensis) horn keratin, qualitatively characterizes the effects of a tapered spiral geometry (the same form as in a ram’s horn) on pressure wave and impulse mitigation, describes the stress attenuation capabilities and features of a ram’s head, and compares the structures and mechanical properties of some energy absorbent natural materials. The results and ideas presented herein can be used in the development of lightweight, energy absorbent, bio-inspired material designs. Among the most notable conclusions garnered from this research include: Horn keratin behaves in an anisotropic manner similar to a long fiber composite. Moisture content dominates the material behavior of horn keratin more than anisotropy, age, and stress-state. This makes moisture content the most influential parameter on the mechanical behavior of horn keratin. Tapered geometries mitigate the impulse generated by a stress wave due to the convergent boundary and a continually decreasing cross sectional area such that greater uniaxial stresses and subsequent axial deformation arises. Furthermore, the tapered geometry introduces small shear stresses that further decrease the impulse. Spiral geometries attenuate the impulse generated by a stress wave by the introduction of shear stresses along the length of the spiral. These shear stresses introduce transverse displacements that function to lessen the impulse. When both a taper and spiral geometry are used in a design, their synergistic effects multiplicatively reduce the impulse Tough natural materials have a high porosity, which makes them light-weight, while increasing their compressive energy absorption ability. Biomaterials whose functions include protection and energy absorption feature a multiscale, hierarchical, composite structure. The constituent materials are arranged in such ways to achieve a synergistic effect, where the properties of the composite exceed the properties of its constituents. Biological materials are therefore not confined to the law of mixtures.

URI

https://hdl.handle.net/11668/17893

Comments

Energy Absorption||FEA||Bio-Inspired Design||Structure-Property Relations||Biomimicry--Research.||Absorption (Physiology)--Research.||Pressure--Measurement.||Bighorn sheep--Research.||Sheep as laboratory animals.||Strains and stresses--Research.||Biomechanics--Research.||Horns--Research.||Keratin--Research.||Attenuation (Physics)--Research.||Shock waves--Computer simulation.||Animal models in research.||Animal experimentation.

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