Local waiting time fluctuations along a randomly pinned crack front

TL;DR

This study investigates the local fluctuations in waiting times along a crack front in a heterogeneous material, revealing power-law distributions and anisotropic avalanche clusters that inform about crack front roughness.

Contribution

It provides a detailed analysis of local waiting time fluctuations and avalanche dynamics along a crack front, linking these to the roughness exponent of the crack line.

Findings

Velocity distribution follows a power law with exponent 2.55.

Burst size distribution follows a power law with exponent 1.7.

Avalanche clusters become anisotropic beyond a certain disorder scale.

Abstract

The propagation of an interfacial crack along a heterogeneous weak plane of a transparent Plexiglas block is followed using a high resolution fast camera. We show that the fracture front dynamics is governed by local and irregular avalanches with very large size and velocity fluctuations. We characterize the intermittent dynamics observed, i.e. the local pinnings and depinnings of the crack front which trigger a rich burst activity, by measuring the local waiting time fluctuations along the crack front during its propagation. The local front line velocity distribution deduced from the waiting time analysis exhibits a power law behavior, $P(v) \propto v^{-\eta}$ with $\eta = 2.55 \pm 0.15$, for velocities $v$ larger than the average front speed $<v>$. The burst size distribution is also a power law, $P(S)\propto S^{-\gamma}$ with $\gamma=1.7 \pm 0.1$. Above a characteristic length scale of disorder $L_d \sim 15 \mu m$, the avalanche clusters become anisotropic, and the scaling of the anisotropy ratio provides an estimate of the roughness exponent of the crack front line, $H=0.66$, in close agreement with previous independent estimates.