Contact info:I successfully defended my Ph.D. dissertation on March 31, 2003, and have since moved on from the LTB lab to gainful employment. Many thanks to my advisor, Bob Behringer, who fosters unbridled creativity, no matter what time of night (morning) it may occur. I can currently be reached by email at hartley_@_phy.duke.edu (replace "_@_" with "@" to pass the spam-filter). Scientific inquiries are welcome. When the email account is shut off, the snail-mail address for the department is: Robert R. Hartley, c/o Department of Physics Duke University Durham, NC 27707-0305 | |
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Research Conducted at Duke | |
Thesis: Robert R. HartleyThe full thesis can be downloaded here. Warning, the file is 5.5MB in size. I have compiled single-spaced version for onscreen reading ease, here. Table of contents:
Abstract iv
Acknowledgements v
1 Prelude 1
1.1 Granular materials: easy to define, difficult to classify, & important to
study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Background 6
2.1 Statics of frictional materials . . . . . . . . . . . . . . . . . . . . .. 6
2.2 Microscopic to continuum descriptions of matter . . . . . . . . . . . . . 9
2.2.1 Microscopic models . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.2 Macroscopic models . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.3 Mesoscopic models . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2.4 Predictions of response . . . . . . . . . . . . . . . . . . . . . . 13
2.3 Janssen description of a granular column . . . . . . . . . . . . . . . . 15
2.4 Granular particles and the contact problem . . . . . . . . . . . . . . . 17
2.5 Kinetic frictional properties . . . . . . . . . . . . . . . . . . . . . . .18
2.6 Evolution of frictional properties . . . . . . . . . . . . . . . . . . . . 19
2.7 Motivation & history . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3 Experimental techniques 30
3.1 Photoelasticity and polariscope optics . . . . . . . . . . . . . . . . . . 30
3.1.1 Light in a birefringent material . . . . . . . . . . . . . . . . . 30
3.1.2 Quantitative measurements of stress . . . . . . . . . . . . . . 32
3.2 Physical properties of the granular particles . . . . . . . . . . . . . . 36
3.3 2D Couette geometry apparatus . . . . . . . . . . . . . . . . . . . . . 36
3.4 2D granular piston apparatus . . . . . . . . . . . . . . . . . . . . . . 40
3.5 Qualitative description of the force network . . . . . . . . . . . . . . 41
4 2-D annular shear experiments 46
4.1 Preparation of the ensembles . . . . . . . . . . . . . . . . . . . . . . . 46
4.2 Mean properties of stress time-series . . . . . . . . . . . . . . . . . . 47
4.3 Possible mechanism for strengthening with rate . . . . . . . . . . . . 55
4.3.1 Shear and hold: plastic deformation . . . . . . . . . . . . . . . 55
4.3.2 Compress and hold: elastic deformation . . . . . . . . . . . . . 61
4.4 Fluctuations in stress . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.5 Distributions of stress . . . . . . . . . . . . . . . . . . . . . . . . . .68
4.6 Stress avalanches . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73
4.6.1 The stress rate of change . . . . . . . . . . . . . . . 73
4.6.2 Avalanches of stress . . . . . . . . . . . . . . . . . 76
4.7 Effects of system size: comparison of small, medium, & large systems 83
4.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5 2-D granular piston 85
5.1 Static configuration of grains in a hopper . . . . . . . . . . . . . . . . 86
5.1.1 Hydrostatic Head . . . . . . . . . . . . . . . . . . . . . . . . . 86
5.1.2 Stress distributions . . . . . . . . . . . . . . . . . . . . . . . . 94
5.1.3 Response to a load . . . . . . . . . . . . . . . . . . . . . . . . 100
5.1.4 Hysteresis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
5.1.5 Stress saturation with depth . . . . . . . . . . . . . . . . . . . 113
5.2 Pushed granular material . . . . . . . . . . . . . . . . . . . . . . . . . 115
5.2.1 Measurements of global stress . . . . . . . . . . . . . . . . . . 116
5.2.2 Varying stress with depth . . . . . . . . . . . . . . . . . . . . 123
5.2.3 Varying stress with width . . . . . . . . . . . . . . . . . . . . 126
5.2.4 Pressure propagation . . . . . . . . . . . . . . . . . . . . . . . 133
5.2.5 Velocity (in)dependence . . . . . . . . . . . . . . . . . . . . . 135
5.3 Behind the looking glass (or the experiment without polarizers) . . . 135
5.3.1 Dilatency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
5.3.2 Velocity fields and convection . . . . . . . . . . . . . . . . . 139
5.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
6 Summary and conclusions 145
6.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
6.1.1 Results of the Couette experiments . . . . . . . . . . . . . . . 145
6.1.2 Results of the piston experiments . . . . . . . . . . . . . . . . 146
6.2 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .147
6.3 Postlude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
Bibliography 151
Biography 163
PPS slides from a talk I gave at SAIC, in Chantilly, VA | |
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Useful links while doing research: |
Other personal research pursuits |
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