Atomistic-level study of the mechanical behavior of amorphous and crystalline silica nanoparticles

Abstract

Molecular dynamics method was used to simulate and investigate the mechanical behavior of amorphous and crystalline silica during nanoindentation and uniaxial compression tests in the nanoscale. Also, the hardness and elastic moduli were experimentally checked by nanoindentation tests. The MD nanoindentation simulation results show that the amorphous silica has an indentation modulus less than the crystalline one, and the elastic strain of the amorphous silica is higher than crystalline silica. In contrast, the amorphous silica has a lower hardness. The uniaxial compression test results show that both structures have three deformation stages during the tests. The first stage corresponds to the linear elastic region; the second stage indicates the elastic-plastic region for crystalline silica, and yielding stage in the amorphous silica. The last stage corresponds to the fracture region for crystalline structure and densification for the amorphous structure. By comparing the area under stress-strain curves of the two structures, it can be concluded that the absorbed energy under external stress in the amorphous silica is three times greater than that in the crystalline one. Moreover, the nanoindentation tests of SPS samples made of amorphous and crystalline silica were performed, and the results confirmed that the crystalline silica has higher hardness and indentation modulus than the amorphous silica. Also, comparing the indentation moduli obtained by simulation and experimental tests shows that the indentation modulus predicted by simulation is in good agreement with that obtained based on experimental results.