Influence of Micro- and Crystalline-Scale Properties on the Fracture of Silica Sand Particles Using 3D Finite-Element Analysis

Particle fracture significantly influences the constitutive behavior of sands and impacts many geotechnical engineering applications, such as hydraulic fracturing, pile driving, blast loading, and stability of dams. When a confined specimen of sand is loaded in 1D compression, particles ultimately fracture, causing permanent microscale deformations that contribute to the yielding behavior of the sand. The most common constituent of sand particles is silica mineral (quartz), which is well known for its natural abundance and high compressive strength. Such excellent properties make silica sand particles an excellent proppant for high-pressure hydraulic fracturing in the oil and gas industry and many other applications. This paper investigates the fracture characteristics of silica sand particles using 3D finite-element (FE) simulations of single particle crushing and confined 1D compression experiments. The 3D FE simulations were generated using digital image processing of in-situ synchrotron microcomputed tomography (SMT) scans, unique 3D meshing algorithms, and coding development in ABAQUS FE software. In-situ SMT images were processed to produce 3D meshes that accurately resemble the complex morphology of the natural sand particles. A material point user-subroutine was developed and implemented in ABAQUS to simulate the constitutive and fracture behaviors of the 3D meshed particles. The user-subroutine incorporates the anisotropic linear elastic behavior of silica mineral and models particle fracture using the principles of continuum damage mechanics. In single-particle crushing, the fracture stress of the sand particle was mostly dependent on the nature of contact between the particle and loading platens. The fracture pattern of the sand particle was mainly influenced by microstructural imperfections and the direction of loading relative to the crystal lattice orientation of the sand particle. In confined 1D compression, the fracture stress of the sand particles correlated well with the particle coordination number and the aspect ratio. Sand particles within the specimen were found to fracture at higher stress levels when they established more contacts with their neighboring particles and exhibited mostly spherical shapes rather than elongated ones. The paper demonstrates the fundamental contribution of micro- and crystalline-scale properties to determine the constitutive and fracture behaviors of silica sand particles.