Crack Front Segmentation and Facet Coarsening in Mixed-Mode Fracture

TL;DR

This study combines microscopy and phase-field simulations to analyze how mixed-mode loading causes crack fronts to segment into facets and coarsen, revealing a subcritical bifurcation and a self-similar coarsening process.

Contribution

It provides new insights into the bifurcation behavior and coarsening dynamics of crack facets under mixed-mode loading, bridging experimental and theoretical findings.

Findings

Bifurcation from planar to segmented crack front is strongly subcritical.

Facet coarsening is driven by a spatial period-doubling instability.

Growth rate of coarsening depends on mode mixity.

Abstract

A planar crack generically segments into an array of "daughter cracks" shaped as tilted facets when loaded with both a tensile stress normal to the crack plane (mode I) and a shear stress parallel to the crack front (mode III). We investigate facet propagation and coarsening using in-situ microscopy observations of fracture surfaces at different stages of quasi-static mixed-mode crack propagation and phase-field simulations. The results demonstrate that the bifurcation from propagating planar to segmented crack front is strongly subcritical, reconciling previous theoretical predictions of linear stability analysis with experimental observations. They further show that facet coarsening is a self- similar process driven by a spatial period-doubling instability of facet arrays with a growth rate dependent on mode mixity. Those results have important implications for understanding the failure of a wide range of materials.