Mechanisms of deformation and instability in crystalline rocks at the pore scale
Abstract/Contents
- Abstract
- Deformation mechanisms at the pore scale are responsible for producing large strains in porous rocks. They include cataclastic flow, dislocation creep, dynamic recrystallization, diffusive mass transfer, and grain boundary sliding, among others. In this work, we focus on two dominant pore-scale mechanisms resulting from purely mechanical, isothermal loading: crystal plasticity and micro-fracturing. We examine the contributions of each mechanism to the overall behavior at a scale larger than the grains but smaller than the specimen, which is commonly referred to as the mesoscale. Crystal plasticity is assumed to occur as dislocations along the many crystallographic slip planes, whereas micro-fracturing entails slip and frictional sliding on microcracks. It is observed that under combined shear and tensile loading, micro-fracturing generates a softer response compared to crystal plasticity alone, which is attributed to slip weakening where the shear stress drops to a residual level determined by the frictional strength. For compressive loading, however, micro-fracturing produces a stiffer response than crystal plasticity due to the presence of frictional resistance on the slip surface. Behaviors under tensile, compressive, and shear loading invariably show that porosity plays a critical role in the initiation of the deformation mechanisms. Both crystal plasticity and micro-fracturing are observed to initiate at the peripheries of the pores, consistent with results of experimental studies. We next develop a computational framework that captures the microfracture processes triggering shear band bifurcation in porous crystalline rocks. The framework consists of computational homogenization on a representative elementary volume (REV) that upscales the pore-scale microfracture processes to the continuum scale. The assumed enhanced strain (AES) finite element approach is used to capture the discontinuous displacement field generated by the microfractures. Homogenization at the continuum scale results in incrementally nonlinear material response, in which the overall constitutive tangent tensor varies with the stress state as well as with the loading direction. Continuum bifurcation detects the formation of a shear band on the REV level; 3D strain probes, necessitated by the incremental nonlinearity of the overall constitutive response, determine the most critical orientation for shear band bifurcation. Numerical simulations focus on microfracturing at the pore scale with either predominant interface separation or predominant interface contact modes. Results suggest a non-associative overall plastic flow and shear band bifurcation that depends on the microfracture length and the characteristic sliding distance related to slip weakening.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2015 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Tjioe, Martin |
|---|---|
| Associated with | Stanford University, Department of Civil and Environmental Engineering. |
| Primary advisor | Borja, Ronaldo Israel |
| Thesis advisor | Borja, Ronaldo Israel |
| Thesis advisor | Deierlein, Gregory G. (Gregory Gerard), 1959- |
| Thesis advisor | Linder, Christian, 1949- |
| Advisor | Deierlein, Gregory G. (Gregory Gerard), 1959- |
| Advisor | Linder, Christian, 1949- |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Martin Tjioe. |
|---|---|
| Note | Submitted to the Department of Civil and Environmental Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2015. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2015 by Martin Tjioe
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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