The direct observation of the core region of a propagating fracture crack in glass

We present the first direct observation (at the nanometre scale) of the far end of a crack tip during propagation. This is achieved by use of an Atomic Force Microscope (AFM) in the case of the so-called brittle fracture. Beside the expected elastic deformation of the surface, the data analysis suggests that a plastic behaviour may take place in the vicinity of the flaw, over a distance of about 50 nm. Also, the experimental method presented here permits to accurately follow the motion (velocity and path) of the crack in the sub-critical regime; consequently, this approach is very likely to be of broad interest in the field of fracture.