Discrepancy between subcritical and fast rupture roughness: A cumulant analysis

Rough crack fronts in a sheet of paper, obtained during a creep experiment, do not follow true scaling laws. Local roughness exponents are estimated using the first order cumulant, a quantity recently introduced in the turbulence literature [J. Delour, J. F. Muzy, and A. Arneodo, Eur. Phys. J. B 23, 243 (2001)]. Using a large data set (102 fronts), we find a significant difference in local roughness between the slow (subcritical) and the fast growth regime.