Experimental investigation of damage and fracture in glassy materials at the nanometre scale

Slow crack advance is observed in real time via an Atomic Force Microscope in a minimal glass, amorphous Silica, under stress corrosion. Fracture proceeds through the nucleation, growth and coalescence of damage cavities, as recently reported in an aluminosilicate glass. The crack growth velocity as observed at the continuum scale is shown to be dominated by accelerating phases corresponding to the cavity coalescence with the main crack front. The process zone at the crack tip is then determined, and shown to increase with time when both the average crack growth velocity and the mechanical stress are kept constant. Transport of water molecules within the process zone is conjectured to be the dominant mechanism responsible for this time evolution. Migration of alkali Na ions in more complex Silicate glass is finally evidenced at the sub-mocrometric scale by observing through AFM the crack propagation in binary Na(2)O/SiO(2) glasses.