Award Date

8-1-2020

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geoscience

First Committee Member

Pamela Burnley

Second Committee Member

Michael Wells

Third Committee Member

Wanda Taylor

Fourth Committee Member

Ashkan Salamat

Number of Pages

161

Abstract

Stress conditions leading to rock deformation influence how a rock will ultimately deform. However, the internal distribution of stress in an elastically anisotropic rock under load, a precursor to rock deformation, is not well understood. Two models that may describe the distribution of stress in polycrystals include the Reuss bound and stress percolation. The Reuss bound, when applied to a polycrystal, describes isostress on each grain resulting in homogeneous intragranular strain and heterogeneous intergranular strain. The stress percolation model involves a network of strong contacts or force chains containing domains of high stress interwoven through areas of lower stress that are heterogeneous at an intragranular and intergranular scale. An experiment has been devised to measure the intragranular stress state of a polycrystal to understand rock deformation. Experimentally measuring stress is possible through Raman spectroscopy, which is capable of quantifying elastic strain changes in a crystal lattice by looking at a change in spectral peak position between a non-loaded and loaded polycrystal. A megapascal load was applied through a uniaxial hand vice equipped with a load cell on a millimeter-sized rectangular parallelepiped consisting of quartz Tiger’s Eye. Spectra were measured on the surface at specific locations on the sample in a loaded and non-loaded state. Stress was calculated at each location, and a stress raster was created to show the stress state of the polycrystalline rock. A grain orientation map using EBSD was collected on the surface of the sample, then overlain with the stress raster, creating the stress map. In several large quartz grains, the map shows an intergranular heterogeneous stress distribution. An interconnecting pattern of raster cells classified as high stress, as well as groups of raster cells classified as low stress, show evidence of an intergranular stress percolation pattern. Results show that the stress distribution in a polycrystalline rock is best modeled by stress percolation.

Keywords

Calcite; Deformation; Elastic; Quartz; Reuss; Stress Percolation

Disciplines

Geology | Geophysics and Seismology

File Format

pdf

File Size

13800 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/


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