Crack front dynamics: the interplay of singular geometry and crack instabilities

TL;DR

This paper investigates the complex dynamics of crack fronts in brittle gels, revealing how local energy balance governs crack behavior and elucidating the formation and termination of micro-branches during rapid crack propagation.

Contribution

It demonstrates that local energy balance accurately describes crack front dynamics even with broken translational symmetry and explains micro-branch formation and cusp development.

Findings

Local energy balance models crack front behavior.

Micro-branches form along localized chains.

Cusp formation leads to micro-branch termination.

Abstract

When fast cracks become unstable to microscopic branching (micro-branching), fracture no longer occurs in an effective 2D medium. We follow in-plane crack front dynamics via real-time measurements in brittle gels as micro-branching unfolds and progresses. We first show that {\em spatially local} energy balance quantitatively describes crack dynamics, even when translational invariance is badly broken. Furthermore, our results explain micro-branch dynamics; why micro-branches form along spatially localized chains and how finite-time formation of cusps along the crack front leads to their death.