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Document Type

Campus Access

Degree Program

Mechanical Engineering

Degree Type

Master of Science (M.S.)

Year Degree Awarded

2009

Month Degree Awarded

February

Keywords

FEA, BITE FORCE, CONTACT ANALYSIS, ANSYS

Abstract

The research in this master's thesis examines the mechanics of primate and early hominid feeding within the context of hypotheses about australopithecine diets. Specifically, this work will be helpful in testing the hypothesis that derived craniodental features in australopithecines are adaptations for feeding on hard, brittle, seasonally available foods. These foods may have been “fallback” items that could be fed upon during periods of scarcity, and thus their consumption may have been ecologically important to survival of early humans.

In order to test the fallback theory, accurate estimates of bite force to initiate a crack in a hard food source using different tooth shapes is essential. These estimates help test the theory in two ways. First, the estimation of bite force for different tooth profiles helps in explaining effect of tooth morphology on fracture of hard food sources. This will test the premise that some species have more efficient tooth shapes for fracturing hard food than other species. Second, the obtained bite force will be used as an input to full scale finite element skull model of different species. Stress and strain distributions in critical regions of the skull will be helpful in understanding feeding adaptations of the different species during evolution.

In this work a fast and accurate finite element analysis method was developed to estimate bite force required to initiate crack in a hard food source like the macadamia nut with different tooth morphologies. The proposed research will help in understanding the effect of tooth shape on the bite force required to initiate a crack in a hard food source

In first experiment we simulated nut biting behavior found in ancient hominid by indenting macadamia nuts with aluminum alloy replicas of primate teeth. Finite element analysis simulation of the biting behavior provided insight into stress profile in the nut at the time of fracture. The results were statistically inconclusive due to huge variation in thickness, diameter and material properties of macadamia nut. In order to study effect of teeth shape on bite force, another study was performed in this work where four different hominoid species namely A.afransis, A.africanus, A.boisei and A.robustus of similar age level, were considered. Cast iron replicas of these hominoid teeth were created. In order to eliminate variability in thickness, diameter and material properties, we used acrylic hemispheres as a macadamia nut substitute. Statistical significance testing and FEA revealed that flatter teeth produces significantly lower force required to fracture acrylic hemisphere as compared to pointed and sharp teeth with comparable fracture stress. Results suggest that pointed teeth produces higher stresses in the food resulting in lower force required to fracture but at the same time stresses in teeth is also high increasing the probability of enamel failure. During the evolution teeth might have evolved to obtain optimum shape which provides tread off between minimum force required to fracture hard food items and minimum stress in enamel to reduce probability of enamel fracture

Past work in estimating bite force is limited to experimental testing. Physical testing of bite force is tedious and time consuming. The proposed combination of physical testing and supporting finite element analysis will be helpful in reducing lengthy physical testing. The main advantage of this method is the comparatively low computational cost and the ability to estimate full field stresses and strains, as opposed to measuring surface strain at specific points. As our modeling and experimental methods become more refined, we anticipate being able to assess the degree to which tooth morphology affects the force needed to fracture hard food items, thereby providing insights into the dietary adaptations of living and extinct primates, including fossil humans.

First Advisor

Ian R. Grosse

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