Dissertation Defense

Start Date: 
Monday, December 19, 2016 - 3:30pm to 5:00pm

GGB 2029

Zhijie Wang

Contact Maturing and Aging of Silica Sand

For more than three decades, sand has been observed to alter its engineering properties over time, but no consensus has been reached on the driving mechanisms behind this phenomenon. Micromechanical behavior at grain scale and the contact scale is coming to be understood as the most plausible cause among the proposals suggested in the available literature, but only very limited research has been conducted at the contact scale in studies of sand aging.

A static fatigue hypothesis is advocated in this thesis; it suggests that delayed fracturing of micro- morphological features on grain surfaces at contacts, such as asperities and mineral debris, is a key contributor to aging of silica sand. To support this hypothesis, this research focuses on exploring micromechanical behavior of inter-grain contacts through micro-scale experiments complemented with numerical simulations.

(1) Micro-scale laboratory experiments were conducted to study time-dependent response of inter-grain contacts under sustained loads; they produced the first set of data of its kind.

(2) Laboratory experiments on sand samples were performed to provide evidence that the contact behavior induces aging effects in sand; factors affecting rates of aging, such as loads, pore fluid acidity, and grain sizes, were explored.

(3) Simulations of a single inter-grain contact were performed with the distinct element method, and possible consequences of contact fatigue/maturation were demonstrated. Finally, a preliminary finite element framework was developed to explore the evolution of grain surface textures to shed light on the effects of pore fluid chemistry on aging rates.

Chair: Radoslaw L. Michalowski

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