New Insight into Mechanical and Thermal Properties of Geomaterials: A Molecular Dynamics Study

Abstract

Due to the recent dramatic increase in computing power available for mathematical modeling and simulation, modern numerical methods play an important role in the analysis of various structural types. Molecular dynamics (MD) and finite element (FE) analysis are one of the most well-developed and popular applications of numerical methods.Silicates are of considerable technological importance because of forming more than 90% of the minerals in the earth’s crust. In addition, the quartz mineral is the major ingredient of silicate particles. In this regard, no published literature has yet investigated the effect of rock particles' crystal structure on their constitutive behavior in nanoscale to explore the effect of particles and fabric on the constitutive behavior of rocks such as crack growth, creep, and fatigue. Molecular dynamics (MD) simulation strives to reinforce experimental predictions and provide insight into the atomistic processes that control examined phenomena as a support of the experimental work and also as a method to fill out the gaps left by laboratory tests. In this dissertation, the analysis of thermo-mechanical properties and the fracture mechanism of crystalline alpha quartz are performed over a wide range of temperatures using MD simulations. For this purpose, a well-known molecular dynamics package (LAMMPS) is employed to investigate the fracture mechanics and crack propagation behavior of 2-D and 3-D crystalline alpha quartz at the atomistic scale. By creating an edge and central crack in the samples and applying uniaxial tensile stress on the material, crack propagation is examined. Moreover, stress-strain behavior of the material, Young’s modulus, fracture toughness, and the effect of grain boundary are identified for different strain rates and crack sizes. According to the results, crystalline alpha quartz shows an anisotropic behavior at the nanoscale, and this anisotropy is regulated by a complicated mechanical process. This knowledge could be utilized to control the crack path and fracture toughness while designing in laboratory experiments and field tests. Besides mechanical properties, crystalline quartz's thermal properties, including thermal conductivity and thermal expansion coefficient, are predicted by using both equilibrium and non-equilibrium molecular dynamics simulations. Also, to explore the effect of forcefields on the results, several interatomic potentials are employed, and the findings are compared.