Dissertation
MESO-SCALE MODELING OF GRADIENT MICRO-STRUCTURE IN SAND: EFFECT OF SIZE AND DISTRIBUTION OF POROSITY
Washington State University
Doctor of Philosophy (PhD), Washington State University
01/2022
DOI:
https://doi.org/10.7273/000004602
Handle:
https://hdl.handle.net/2376/125146
Abstract
Strain concentration at some material points that seem arbitrary- usually called strain localization- is a very common phenomenon in granular media which affects the overall behavior of the material under different scenarios including laboratory tests, failure of natural and man-made slopes, and response of foundations to loading. Classical mathematical models and constitutive equations were mainly based on the elastic behavior of the material and including the post-yielding material behavior and through the plastic region advanced afterwards. More complicated constitutive equations are proposed in recent decades, however, a great portion of them is specified for the behavior of metals. The main objective of this study was to investigate how the distribution of voids and the range of their size in a sand specimen could alter the behavior of the soil as a continuum medium, considering the strain localization behavior (or formation of shear bands) of granular materials in an elastoplastic regime. A gradient plasticity model along with finite element method (FEM) analysis were the main components of this research to model the strain localization in coarse, poorly-graded Ottawa sand. The gradient plasticity model was implemented into ABAQUS using a user-defined code (UMAT) to simulate the effects of various distributions of porosity as pores with different sizes in the behavior of sand under different confining pressures. Different specimens were defined in ABAQUS by keeping the porosity constant but, changing the size and numbers of the holes for different configurations.
To validate the results, existing laboratory experiments data of a biaxial test on a coarse, poorly-graded Ottawa sand, along with previous numerical modeling results were used. The parameters, experiment conditions, and soil properties of the current study were based on the actual biaxial test referred to in the next chapters. The results of this study showed good agreements with experimental studies and theoretical expectations. By increasing the number of voids, which conveys the reduction of their size in order to keep the porosity constant, the specimens showed a broader hardening behavior and less distinct formation of shear bands. Instead of shear bands, slip lines were more observable in these specimens which indicated the diffusion of strain at more points compared to its concentration. A similar trend was detectable by increasing the confining pressure.
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Details
- Title
- MESO-SCALE MODELING OF GRADIENT MICRO-STRUCTURE IN SAND: EFFECT OF SIZE AND DISTRIBUTION OF POROSITY
- Creators
- VAHIDEH TOHIDIKARANDAGH
- Contributors
- Haifang Wen (Advisor)Xianming Shi (Committee Member)Saumya Amarasiri (Committee Member)Sunil Sharma (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Civil and Environmental Engineering, Department of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 145
- Identifiers
- OCLC#: 1365772652; 99900901029701842
- Language
- English
- Resource Type
- Dissertation