Location
University of Nevada, Las Vegas, Science and Education Building
Start Date
9-8-2011 10:15 AM
End Date
9-8-2011 12:00 PM
Description
Determining the reaction of poly-crystalline structures to induced stress is an extremely difficult problem in contemporary engineering and geology. The main challenge lies in the inhomogeneity of the grains inside of the poly-crystalline structures. To predict the response of a certain polycrystalline structure to a specific stress, you must resort to one of two views on grain interaction, an orientation or propagation based model. For every material there may be certain correlations between the prediction model used and the actual deformation that occurred. Our work centers around describing the correlation of these prediction models with a sample of naturally deformed mantle xenolith from the Jagersfontein Mine in South Africa. In order to correlate the models with the sample, we needed to calculate the orientation and dislocation density of the individual grains. To measure the dislocation density, the ratio of the area of the dislocations to the total area of the grain itself, the sample needed to go through a decoration process. The sample was heated to accelerate oxidization and highlight the sample’s dislocations. This “decorating” process allows us to easily discern the dislocations on the surface of the sample using a Scanning Electron Microscope (SEM). Dislocation density can then be calculated by using an open-source image analysis software called ImageJ on the image of the grain. Additionally, the other calculation, the orientation of the grain, is measured by an Electron Backscatter Diffraction (EBSD) analysis of the sample. The EBSD is a process of firing electrons at the sample and reading the diffractions produced. These diffractions create a “picture” of Kikuchi Bands, simply the diffraction lines produced by the electrons, which can be analyzed by proprietary software resulting in a calculation of the orientation of each grain. We were then able to look for correlations between the dislocation density and the orientation of each grain and identify which model describes the deformation results most accurately.
Keywords
Igneous rocks — Inclusions; Rock deformation; Rock mechanics; South Africa – Jagersfontein Mine; Strains and stresses
Disciplines
Geology | Geotechnical Engineering | Mineral Physics
Language
English
Correlation between grain dislocation density and orientation for naturally deformed mantle xenolith from Jagersfontein Mine
University of Nevada, Las Vegas, Science and Education Building
Determining the reaction of poly-crystalline structures to induced stress is an extremely difficult problem in contemporary engineering and geology. The main challenge lies in the inhomogeneity of the grains inside of the poly-crystalline structures. To predict the response of a certain polycrystalline structure to a specific stress, you must resort to one of two views on grain interaction, an orientation or propagation based model. For every material there may be certain correlations between the prediction model used and the actual deformation that occurred. Our work centers around describing the correlation of these prediction models with a sample of naturally deformed mantle xenolith from the Jagersfontein Mine in South Africa. In order to correlate the models with the sample, we needed to calculate the orientation and dislocation density of the individual grains. To measure the dislocation density, the ratio of the area of the dislocations to the total area of the grain itself, the sample needed to go through a decoration process. The sample was heated to accelerate oxidization and highlight the sample’s dislocations. This “decorating” process allows us to easily discern the dislocations on the surface of the sample using a Scanning Electron Microscope (SEM). Dislocation density can then be calculated by using an open-source image analysis software called ImageJ on the image of the grain. Additionally, the other calculation, the orientation of the grain, is measured by an Electron Backscatter Diffraction (EBSD) analysis of the sample. The EBSD is a process of firing electrons at the sample and reading the diffractions produced. These diffractions create a “picture” of Kikuchi Bands, simply the diffraction lines produced by the electrons, which can be analyzed by proprietary software resulting in a calculation of the orientation of each grain. We were then able to look for correlations between the dislocation density and the orientation of each grain and identify which model describes the deformation results most accurately.
Comments
Advisor: Pamela Burnley, UNLV
Research supported by: NSF grant DMR-1005247