Fracture roughness scaling: A case study on planar cracks

Using a multi-resolution technique, we analyze large in-plane fracture fronts moving slowly between two sintered Plexiglas plates. We find that the roughness of the front exhibits two distinct regimes separated by a crossover length scale delta*. Below delta*, we observe a multi-affine regime and the measured roughness exponent. zeta(-)(parallel to) = 0.60 +/- 0.05 is in agreement with the coalescence model. Above delta*, the fronts are mono-affine, characterized by a roughness exponent. zeta(+)(parallel to) = 0.35 +/- 0.05, consistent with the fluctuating line model. We relate the crossover length scale to fluctuations in fracture toughness and the stress intensity factor. Copyright (C) EPLA, 2010