Development of Roughness in Crack Propagation

We report on the statistical analysis of experimental measurements of the crack roughness for a fracture initiated from a straight notch in a granite sample. The crack surface is shown to develop a self-affine character over a correlation length ξ which depends on the distance to the notch y as a power law ξ ∝ y α characterized by a dynamic exponent 1/α estimated to be 1.2 ± 0.15. The self-affine roughness exponent below the correlation length is found to be 0.80 ± 0.05. The scaling is obtained from two maps of the surface, consisting each in more than 10 5 data points.