Pinning/depinning of crack fronts in heterogeneous materials

TL;DR

This study investigates the roughness and scaling behavior of crack fronts in heterogeneous materials, revealing two distinct regimes with different roughness exponents and a velocity-dependent crossover length.

Contribution

It identifies two fracture regimes with universal and material-specific roughness signatures and characterizes their dependence on crack velocity and applied force.

Findings

Universal roughness index of 0.78 at large scales

Crossover length decreases as velocity increases, following a power law

Exponents for force dependence are approximately 2

Abstract

The fatigue fracture surfaces of a metallic alloy, and the stress corrosion fracture surfaces of glass are investigated as a function of crack velocity. It is shown that in both cases, there are two fracture regimes, which have a well defined self-affine signature. At high enough length scales, the universal roughness index 0.78 is recovered. At smaller length scales, the roughness exponent is close to 0.50. The crossover length $\xi_c$ separating these two regimes strongly depends on the material, and exhibits a power-law decrease with the measured crack velocity $\xi_c \propto v^{-\phi}$, with $\phi \simeq 1$. The exponents $\nu$ and $\beta$ characterising the dependence of $\xi_c$ and $v$ upon the pulling force are shown to be close to $\nu \simeq 2$ and $\beta \simeq 2$.