Fig. 1. Normal stress (a) and maximum shear stress (b) as a function of strain for different silica glass samples (S1–S5). Three stages are displayed, and hardening tendency increases with initial densification.

Fig. 2. Pressure-density relation for silica glass samples: present study compared with the experiments. Curves S1–S5: under uniaxial compression; circle and triangle: hydrostatic experimental data obtained by Meade et al.^[38] and Sato et al.;^[39] square and pentagon: shock experimental data obtained by Renou et al.^[21] and Sugiura et al.^[41] Yield pressure of densified silica glass ranges from 5 to 12 GPa. All curves converge at 12 GPa.

Fig. 3. Density as a function of pressure for S1 during uniaxial loading-unloading. Densification and hysteresis are both shown. A, B, C, D and E correspond to strains of 0.1, 0.2, 0.3, 0.4, and 0.5, respectively. The solid line represents the loading path, and the dotted lines are the unloading paths.

Fig. 4. RDFs of Si–O (a) Si–Si (b) O–O (c) for S1 at different strains. RDFs of Si–O (d) Si–Si (e) O–O (f) for glass unloaded from different strains. The arrows indicate the change of the peak position. The RDFs of the unloaded sample are consistent with the initial state.

Fig. 5. BADs of Si–O–Si (a) O–Si–O (b) for S1 at different strains. BADs of Si–O–Si (c) O–Si–O (d) for glass unloaded from different strains. The arrows indicate the change of the peak position. The Si–O–Si bond angle of silica glass unloaded from the inelastic region becomes smaller.

Fig. 6. Si–O coordination number curves of S1 at different strains. The average coordination number of Si–O increases with strain from 4 to around 6.

Fig. 7. (a) Fractions of 4-fold, 5-fold, 6-fold coordinated Si atoms versus strain. Pink atoms: Si, blue atoms: O in the insert figure). Here 5-fold Si increases linearly with strain in plastic region and 6-fold Si increases mainly in hardening region. (b) Color micrographs of Si atoms according to the coordination number CN color bar. The figure only includes Si atoms. The cutoff distance for coordination is set to 2.4 Å.

Fig. 8. (a) Average atomic displacement as a function of strain, and (b) microstructure of atoms in X–Y plane at different strains according to the R(i) color bar. The law of atomic lateral diffusion during uniaxial compression is shown.

Fig. 9. The density of recovered glass at 0 GPa as a function of the maximum strain reached. Results for all the samples are displayed.

Fig. 10. Density as a function of pressure for S3 (a) and S5 (b) during uniaxial loading-unloading. Solid and hollow triangles represent the hydrostatic experimental data on compression and decompression obtained by Sato et al.^[42].

Fig. 11. BADs of Si–O–Si (a) O–Si–O (b) for the initial state, 0.3 strain, unloaded state of S5. The arrows indicate the change of the peak position. The Si–O–Si bond angle becomes smaller.