Micromechanical Analysis of Stresses and Instabilities in Wet Granular Materials: Homogenization and Discrete Element Approaches
Date
2023-10-30
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Abstract
This thesis presents the micromechanical analysis of wet granular material behavior within the pendular regime where particles are held by distinct liquid bridges through the action of capillarity and thin film adhesion. The presence of air and liquid phases within the pore space of solid particles significantly impacts the mechanical properties of wet geomaterials, and hence their failure behavior as a material instability phenomenon. The first question is how does the stress transport to the different phases (air, water, and solid) as a function of the internal microstructural construct and interfaces? An analytical expression of the internal stress partitioning between air, water and solid is formally derived via a homogenization scheme which upscales the interfacial surface tension physics at the pore scale to the macroscopic (specimen) scale. Focusing particularly on fine particles in the micrometer range, the study encompasses the two dominant mechanisms in wet conditions: adsorption and capillarity. These mechanisms consider the role of adsorbed liquid films governed by a disjoining pressure and liquid bridges arising from matric suction as a water potential. The final derivation reveals the tensorial nature of an adsorptive-capillary stress variable that is closely linked to the topology of the fluid partitions in the pore network, and is hence non-spherical. The next question is, among the various stress components, how does the contact (solid skeleton) stress tensor relate to the strain tensor to describe the constitutive behavior of wet granular materials? A multi-directional probing numerical experiment on a Representative Element Volume (REV) is implemented in Discrete Element Method (DEM) simulations to link increments of stresses to increments of strains through a bridging of grain/pore scale and the REV scale. Essentially, the incremental constitutive tangent operator is reconstructed through a perturbation analysis. This methodology also offers the possibility of micromechanically investigating bifurcation phenomena somewhat unexplored for partially saturated conditions. As a result, aspects of material instability, failure mechanisms, and shear band localization are examined by probing into the spectral characteristics of the micromechanically and hydromechanically informed tangent operator and the second-order work instability criterion for both dry and wet states.
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Wet Granular Materials, Micromechanics, Partially Saturated, Stress Transmission, Instability, Localization
Citation
Farahnak Langroudi, M. (2023). Micromechanical analysis of stresses and instabilities in wet granular materials: homogenization and discrete element approaches (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.