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

摘要

We have studied the propagation of a crack front along the heterogeneous weakplane of a transparent poly(methyl methacrylate) (PMMA) block using twodifferent loading conditions: imposed constant velocity and creep relaxation.We have focused on the intermittent local dynamics of the fracture front for awide range of average crack front propagation velocities spanning over fourdecades. We computed the local velocity fluctuations along the fracture front.Two regimes are emphasized: a depinning regime of high velocity clustersdefined as avalanches and a pinning regime of very low-velocity creeping lines.The scaling properties of the avalanches and pinning lines (size and spatialextent) are found to be independent of the loading conditions and of theaverage crack front velocity. The distribution of local fluctuations of thecrack front velocity are related to the observed avalanche size distribution.Space-time correlations of the local velocities show a simple diffusion growthbehavior.