Molecular simulation of subcritical crack growth under dry conditions in a model brittle glass

Abstract

Subcritical crack growth can occur under a constant applied load below the threshold value for catastrophic failure, also known as static fatigue. Here, we report how a crack grows under a combination of stress-intensity factor (K) and temperature in a model brittle glass using molecular dynamics simulations. The model glass is under dry conditions, thus avoiding the complexity of corrosion chemistry. The crack growth rate is shown to be inconsistent with the commonly used subcritical crack growth model rooted in the transition state theory (TST), in which the applied stress-intensity factor reduces the transition barrier. A new subcritical crack growth model is proposed with a constant barrier and a K-dependent prefactor in TST, representing the size of the region for potential bond breaking. The thermomechanical condition for subcritical crack growth is also mapped in the K-T domain, in between elastic deformation and catastrophic fracture regimes. Finally, we show substantial crack self-healing once the applied load is removed, under the thermodynamic driving force of surface energy reduction. Our findings provide new insights into the mechanochemical coupling during static fatigue and call for experimental investigation of whether the activation energy is K-dependent.