Résumé:

By investigating more than six decades of length scales (from nm to mm), we have studied how linear elastic well-known solutions hold water at the close neighbourhood of the tip of a crack propagating in oxide glass under stress-corrosion regime. The existence of dissipative mechanisms at small scale was especially targeted. Subcritical crack propagation was performed by a loading cell on Double Cleavage Drilled Compression samples under controlled atmosphere. Post-mortem and in-situ observations were performed by optical techniques and atomic force microscopy (AFM). A 2D/3D analysis of this sample was realized according to linear elastic fracture mechanics in order to discuss the experimental results and to ensure the mechanical test control at all scales. The mechanical effect of capillary condensation observed by AFM at the crack tip was modelled according to a cohesive zone model. This allowed notably to evaluate the negative Laplace pressure in the liquid and to explain the crack closure mechanism in glass. A digital image correlation technique was used on series of consecutive AFM in-situ images. We showed that the elastic solution for the surface displacement field is valid up to a distance of 10 nm from the crack tip. The height correlation functions along the AFM images of fracture surfaces were also analyzed. We showed that the cut-off length, found close to few tens of nanometres and previously interpreted as the process zone size, is most probably due to the finite size of the AFM scanning probe and in agreement with the DIC, no process zone larger than 20 nm is observable.