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 th e far end of a crack tip during propagation. This is achieved by use o f an Atomic Force Microscope (AFM) in the case of the so-called brittl e fracture. Beside the expected elastic deformation of the surface, th e data analysis suggests that a plastic behaviour may take place in th e vicinity of the flaw, over a distance of about 50 nm. Also, the expe rimental method presented here permits to accurately follow the motion (velocity and path) of the crack in the sub-critical regime; conseque ntly, this approach is very likely to be of broad interest in the fiel d of fracture.