Fracture of silicate glasses: Micro-cavities and correlations between atomic-level properties

TL;DR

This study uses large-scale simulations to explore how composition affects the fracture behavior of silicate glasses, revealing differences in brittleness, crack velocity, and cavity formation linked to sodium content.

Contribution

It provides new insights into the microscopic mechanisms of glass fracture, highlighting the role of local heterogeneity and composition-dependent nanoductility.

Findings

Silica glass is brittle; Na-rich glasses show ductility.

Crack velocity decreases with higher Na concentration.

Na-rich glasses form nanocavities ahead of the crack.

Abstract

We use large-scale simulations to investigate the dynamic fracture of silica and sodium-silicate glasses under uniaxial tension. The stress-strain curves demonstrate that silica glass is brittle whereas the glasses rich in Na show pronounced ductility. A strong composition dependence is also seen in the crack velocity which is on the order of 1800 m/s for glasses with low Na concentration and decreases to 700 m/s if the concentration is high. We find that during the fracture of Na-rich glasses very irregular cavities as large as 3-4 nm form ahead of the crack front, indicating the presence of nanoductility in these glasses. Before fracture occurs, the local composition, structure, and mechanical properties are heterogeneous in space and show a strong dependence on the applied strain. Further analysis of the correlations between these local properties allows to obtain a better microscopic understanding of the deformation and fracture of glasses and how the local heating close to the crack tip, up to several hundred degrees, permits the structure to relax.