Résumé
We study the roughness properties of fracture surfaces obtained by sub-critical fracture of silica glass in a double-cleavage-drilled-compression (DCDC) setup under controlled velocity, stress intensity factor and relative humidity. We extract the topography of these surfaces using an atomic force microscope and study their roughness properties using two different indicators. On the one hand, we find that the root-mean-square roughness Rq decreases linearly with the stress intensity factor K1, or equivalently with the logarithm of the crack velocity at fixed relative humidity, as previously reported, while no significant dependence on relative humidity at fixed K1 is observed. On the other hand, we study the 1D height-height correlation functions. Recent work on fracture surfaces has shown that the lower cut-off in the asymptotic self-affine regime of this function is related to the size of the process zone. Here we show that the cut-off we find is caused by the finite size of the probe.