Crack fronts and damage in glass at the nanometer scale

TL;DR

This study investigates nanometer-scale crack propagation in glass, revealing nano-ductile fracture behavior through real-time microscopy, influenced by heterogeneities and damage cavity dynamics at low velocities.

Contribution

It is the first to observe crack progression via nanometric damage cavities in glass, linking nano-ductile fracture mechanisms to low-temperature conditions.

Findings

Crack propagation involves nucleation, growth, and coalescence of nanometric cavities.

Heterogeneities influence crack velocity and behavior.

Nano-ductile fracture mode observed at temperatures below glass transition.

Abstract

We have studied the low speed fracture regime for different glassy materials with variable but controlled length scales of heterogeneity in a carefully mastered surrounding atmosphere. By using optical and atomic force microscopy (AFM) techniques we tracked in real-time the crack tip propagation at the nanometer scale on a wide velocity range (mm/s - pm/s and below). The influence of the heterogeneities on this velocity is presented and discussed. Our experiments reveal also -for the first time- that the crack progresses through nucleation, growth and coalescence of nanometric damage cavities within the amorphous phase. This may explain the large fluctuations observed in the crack tip velocities for the smallest values. This behaviour is very similar to what is involved, at the micrometric scale, in ductile fracture. The only difference is very likely due to the related length scales (nanometric instead of micrometric). Consequences of such a nano-ductile fracture mode observed at a temperature far below the glass transition temperature in glass is finally discussed.