Local dynamics of a randomly pinned crack front during creep and forced propagation: An experimental study

TL;DR

This experimental study investigates the local dynamics of crack front propagation in PMMA under different loading conditions, revealing scale-invariant avalanche and pinning regimes with consistent statistical properties.

Contribution

It provides new insights into the scale-invariant behavior of crack front dynamics and their independence from loading conditions and average velocities.

Findings

Avalanche and pinning regimes are statistically independent of loading conditions.

Distribution of local velocity fluctuations correlates with avalanche sizes.

Space-time correlations exhibit simple diffusion growth behavior.

Abstract

We have studied the propagation of a crack front along the heterogeneous weak plane of a transparent poly(methyl methacrylate) (PMMA) block using two different loading conditions: imposed constant velocity and creep relaxation. We have focused on the intermittent local dynamics of the fracture front for a wide range of average crack front propagation velocities spanning over four decades. We computed the local velocity fluctuations along the fracture front. Two regimes are emphasized: a depinning regime of high velocity clusters defined as avalanches and a pinning regime of very low-velocity creeping lines. The scaling properties of the avalanches and pinning lines (size and spatial extent) are found to be independent of the loading conditions and of the average crack front velocity. The distribution of local fluctuations of the crack front velocity are related to the observed avalanche size distribution. Space-time correlations of the local velocities show a simple diffusion growth behavior.