Molecular dynamics simulation of amorphous silica under uniaxial tension: From bulk to nanowire

Abstract

Molecular dynamics (MD) simulations were carried out to study bulk silica glass and amorphous silica nanowire under uniaxial tension. Periodic boundary conditions were employed to mimic infinite bulk samples. Cutting and casting methods were used to prepare nanowires. Our study shows that simulation parameters, such as system size, cooling rate, working temperature and strain rate, need to be carefully chosen in order to correctly reproduce the brittle fracture behavior of amorphous silica. The stiffness of silica glass is less sensitive to these parameters than the tensile strength and the failure strain. However, the sample density and the anomalous nonlinear elasticity of silica glass should be correctly taken into account to get an accurate estimate of its stiffness from MD simulations. Our study also shows that, with proper simulation parameters, amorphous silica nanowires down to 1nm in radius still exhibits a brittle fracture behavior. Nanowires prepared by the cutting method have a lower stiffness and tensile strength but a higher failure strain than the cast ones, due to more surface defects generated during the cutting process at low temperatures. Defects-induced ductility could be an effective way to make less brittle nanostructures of amorphous silica.