Energy dissipation at the atomic scale explains how fracture energy depends on crack velocity in silica glass

TL;DR

This study uses molecular dynamics simulations to reveal that fracture energy in silica glass increases with crack velocity due to nanoscale surface changes, challenging the notion of constant fracture energy.

Contribution

It demonstrates that fracture energy varies with crack velocity at the atomic scale, influenced by nanoscale roughening and surface energy changes, not just surface area.

Findings

Fracture energy increases by up to 33% below the branching threshold.

Nanoscale roughening contributes equally to fracture energy rise as surface energy density.

Dynamic fracture creates fundamentally different surfaces at the nanoscale.

Abstract

The fracture energy of brittle materials rises with crack velocity, and this effect is typically attributed to surface roughening from path instabilities. Here we show, using molecular dynamics simulations of silica glass with a first-principles machine learned interatomic potential, that the structural fracture energy rises by up to 33 % already below the branching threshold, showing that fracture energy is not a constant material property. This rise in fracture energy is roughly equally partitioned between an increase in the intrinsic surface energy density and nanoscale roughening that increases the real fracture surface area. Results demonstrate that dynamic fracture in silica glass increases the fracture energy not merely by creating more apparent surface, but also by creating a fundamentally different surface at the nanoscale.