Rheology, Mechanics and Transport in Granular Materials: A Versatile Computational Framework.
This three-part thesis describes a versatile computational framework for the simulation of rheology, mechanics and thermal transport in soft granular materials. The class of granular materials investigated here comprise of soft, elastic, frictionless grains at dense volume fractions that undergo fluid-to-solid phase transition upon the application of external stress. The first part of this thesis investigates the rheology of soft granular materials. Chapter 2 describes the theory and numerical implementation of a stress-based rheological method to simulate steady-state flow and creep in soft granular materials and granular suspensions under the application of external hydrostatic and shear stress. The methods introduced in Chapter 2 are implemented in Chapter 3 to investigate the micromechanics of creep in soft granular materials that are uniaxially compressed below the yield threshold. The microscopic insights of creep gained in this chapter are applicable to the widely observed phenomena of slow relaxation dynamics in a wide class of amorphous solids including granular matter, foams and colloids. The second part of this thesis investigates the mechanics of jammed granular solids. Chapter 4 describes a variable-cell enthalpy-based numerical method to simulate stress-induced jamming of soft grains, and probe the mechanics of jammed granular solids. The stress-based methods of Chapter 4 are implemented in Chapter 5 to probe the micromechanical response of a jammed granular solid to quasi-static shear stress. The microscopic insights of the observed stick-slip response to external shear has numerous applications ranging from geological study of earthquakes to the mechanics of a wide class of amorphous solids. In Chapter 6 the influence of attractive forces on the mechanics of jammed granular solids is investigated. The third part of this thesis describes a heat conduction model for sub-micron thermal transport in dense nano-granular thermoelectric materials. The jamming methods of Chapter 4 are used to simulate the compaction and sintering of thermoelectric nanoparticles into solid-state devices. An effective medium heat conduction model that incorporates phonon scattering mechanisms in nanoporous microstructures is implemented to analyze effective thermal conductivity of bottom-up manufactured thermoelectric materials.
Fisher, Purdue University.
Mechanics|Mechanical engineering|Materials science
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