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 δ * . Below δ * , we observe a multi-affine regime and the measured roughness exponent ζ || − =0.60±0.05 is in agreement with the coalescence model. Above δ * , the fronts are mono-affine, characterized by a roughness exponent ζ || + =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.