Mechanical and microstructural response of densified silica glass under uniaxial compression: Atomistic simulations*

We investigate the mechanical and microstructural changes of the densified silica glass under uniaxial loading-unloading via atomistic simulations with a modified BKS potential. The stress-strain relationship is found to include three respective stages: elastic, plastic and hardening regions. The bulk modulus increases with the initial densification and will undergo a rapid increase after complete densification. The yield pressure varies from 5 to 12 GPa for different densified samples. In addition, the Si-O-Si bond angle reduces during elastic deformation under compression, and 5-fold Si will increase linearly in the plastic deformation. In the hardening region, the peak splitting and the new peak are both found on the Si-Si and O-O pair radial distribution functions, where the 6-fold Si is increased. Instead, the lateral displacement of the atoms always varies linearly with strain, without evident periodic characteristic. As is expected, the samples are permanently densified after release from the plastic region, and the maximum density of recovered samples is about 2.64 g/cm(3), which contains 15 % 5-fold Si, and the Si-O-Si bond angle is less than the ordinary silica glass. All these findings are of great significance for understanding the deformation process of densified silica glass.