3D Characterization of Force Transmission Structures and the Effect of Particle Scale Properties on the Force Chains in Sand

The mechanics of granular materials at the macro-scale is significantly affected by the particle-scale properties and the complex interaction of particles such as translation, rotation, interlocking, particle morphology, crystal structure, particle size effects, and contact network. Current continuum models do not address the discrete nature of the particles and their interactions and consider them as homogenous materials without any inherent structures. Additionally, models that can account for all of these parameters will be very complex to implement in general multi-scale finite element codes successfully. The limited state of knowledge about the influences of particle-scale properties and their interactions affects the efficiency of such models as well. A comprehensive study of these properties, interactions, and their effects on the mechanics of granular materials can potentially improve the efficiency of micro-scale numerical models that are utilized to simulate the constitutive behavior of granular materials. Particularly, force transmission systems in granular media are affected considerably by the particle-scale properties and the interactions between them. This dissertation employed synchrotron micro-computed tomography (SMT) and 3D x-ray diffraction (3DXRD) microscopy to characterize the crystal structure of individual particles, and the force transmission structures in a specimen of natural Ottawa sand loaded under a 1D confined compression. The evolution of force structures and their properties during different load steps were examined in detail. Statistical methods were employed to investigate the effects of particle properties such as the crystal structure, contact network, and particle morphology on the force transmission structures and their evolution uncovering possible correlations between particle properties, force structures, and particle fragmentation that can be used as predictive measurements to enhance numerical models. The proposed research will provide unique 3D experimental measurements across multiple length scales which can be employed to validate current numerical models and provide an insightful understanding of the mechanisms of force transmission in natural silica sand.