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Nanoindentation Studies of Plasticity and Dislocation Creep in Halite

Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA 19104, USA
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Geosciences 2019, 9(2), 79; https://doi.org/10.3390/geosciences9020079
Received: 31 December 2018 / Revised: 1 February 2019 / Accepted: 3 February 2019 / Published: 6 February 2019
(This article belongs to the Special Issue Micromechanics of Reservoir and Cap Rocks)
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Abstract

Previous deformation experiments on halite have collectively explored different creep mechanisms, including dislocation creep and pressure solution. Here, we use an alternative to conventional uniaxial or triaxial deformation experiments—nanoindentation tests—to measure the hardness and creep behavior of single crystals of halite at room temperature. The hardness tests reveal two key phenomena: (1) strain rate-dependent hardness characterized by a value of the stress exponent of ~25, and (2) an indentation size effect, whereby hardness decreases with increasing size of the indents. Indentation creep tests were performed for hold times ranging from 3600 to 106 s, with a constant load of 100 mN. For hold times longer than 3 × 104 s, a transition from plasticity to power-law creep is observed as the stress decreases during the hold, with the latter characterized by a value of the stress exponent of 4.87 ± 0.91. An existing theoretical analysis allows us to directly compare our indentation creep data with dislocation creep flow laws for halite derived from triaxial experiments on polycrystalline samples. Using this analysis, we show an excellent agreement between our data and the flow laws, with the strain rate at a given stress varying by less than 5% for a commonly used flow law. Our results underscore the utility of using nanoindentation as an alternative to more conventional methods to measure the creep behavior of geological materials. View Full-Text
Keywords: halite; creep; nanoindentation; hardness; plasticity halite; creep; nanoindentation; hardness; plasticity
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Thom, C.A.; Goldsby, D.L. Nanoindentation Studies of Plasticity and Dislocation Creep in Halite. Geosciences 2019, 9, 79.

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