Origin of the elastic anisotropy of silica particles: Insights from first-principles calculations and nanoindentation molecular dynamic simulations

XY Ma and X Kang and JW Cao, COMPUTERS AND GEOTECHNICS, 159, 105489 (2023).

DOI: 10.1016/j.compgeo.2023.105489

To better elucidate and comprehend the origin of the elastic anisotropy observed in silica sand, this study in-vestigates the nanoscale mechanical properties of a-quartz (the main component of silica sand) using the first-principles calculations (density functional theory, DFT) and nanoindentation molecular dynamics (MD) simu-lations. The cell parameters and elastic constants (Cij) of a-quartz are obtained by DFT with PBESOL functional. The electron density difference of the most commonly exposed crystal surfaces 100, 001, and 101, ex-hibits significant distinction, which is considered as the underlying cause of a-quartz's elastic anisotropy. This study reveals a significant difference in Young's modulus E, Poisson's ratio v, and hardness H along different directions, which are also visualized in three dimensional graphics. Notably, E10 0 = 81.576 GPa < E0 0 1 = 101.198 GPa < E1 0 1= 113.323 GPa, and H0 0 1 = 9.068 GPa < H1 0 0= 11.258 GPa < H1 0 1 = 19.870 GPa. The change in E calculated by MD simulations is consistent with DFT calculations. Additionally, this study observed distinct initiation of yielding during nanoindentation for different crystal surfaces, with the corre-sponding indentation yielding depth following the trend D1 0 0 > D0 0 1 > D1 0 1. Furthermore, both DFT and MD simulation results indicate that the negative v effect on E is negligible in a-quartz.

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