Roughness of crack interfaces in two-dimensional beam lattices

The roughness of crack interfaces is reported in quasistatic fracture, using an elastic network of beams with random breaking thresholds. For strong disorders we obtain zeta = 0.86(3) for the roughness exponent, a result which is very different from the minimum energy surface exponent, i.e., zeta = 2 / 3. A crossover to lower values is observed as the disorder is reduced, the exponent in this regime being strongly dependent on the disorder.