Rheology is a branch of study used to describe and assess the deformation, flow, and plastic behavior of solid materials. Plastic deformation naturally occurs in the Earth’s lower crust and upper mantle, governing the nature of plate tectonics. To understand this phenomenon, large-scale deformation studies of rocks are commonly conducted at high temperatures and under large confining pressures, simulating the conditions found in the mantle, to prevent cracking and promote plastic deformation. However, such testing provides limited insight into the local deformation processes occurring at the intracrystalline level, and repeated testing to achieve statistically significant results can be challenging. Nanoindentation, a testing technique from materials science, involves pushing a sharp indenter into a specimen with a precisely controlled amount of force and can be a significant tool in investigating the viscoplastic rheology of geological materials. By pressing a small pyramidal indenter into the rock’s surface at positions of interest, we can probe variations in properties over micron length scales, while the undeformed material surrounding the indent provides a natural constraint against crack formation and growth. This approach can gather information about the hardness and yield strength of the rock at lower temperatures than what have been previously tested with traditional methods. For the scope of this experiment, nanoindentation methods were used to characterize the local plastic deformation behavior of Westerly granite at low temperatures. Westerly granite is composed of quartz and two types of felspar, orthoclase and plagioclase, which are widely abundant in the Earth’s crust. This composition allows for a way to quickly characterize multiple phases and orientations at once, yielding more useful data. The results from studying these minerals can be compared to previously published data to learn more about their properties.

Document Type

Final Report

Author's School

McKelvey School of Engineering

Author's Department

Mechanical Engineering and Materials Science

Class Name

Mechanical Engineering and Material Sciences Independent Study

Date of Submission