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Stress corrosion fracture of glass
Although amorphous silica has a liquid-like homogeneous structure at length scales as short as ∼10 Å, it seems to behave as a disordered material when fractured. Controversial Atomic Force Microscopy experiments have indeed suggested that a stress corrosion crack – which progresses very slowly under the combined action of an external load and of a chemical reaction with the water present in the surrounding atmosphere – propagates through the nucleation, growth and coalescence of nanometric cracks forming ahead of its tip. This “quasi-brittle” fracture mechanism is typical of highly disordered solids such as wood, concrete, or mortars.
Because the presence of water leads to the rupture of Si-O bonds under very moderate external loads, we have probed the quantity of water entered into the glass during the fracture process. For this purpose, we have grown subcritical cracks in a controlled stable way within a saturated heavy water atmosphere. The resulting fracture surfaces were probed with neutron reflection and it was shown that heavy water had actually penetrated into the bulk of the material around the crack tip by 100 Å. Furthermore, the high water concentrations stored within the first 50 Å under the fracture surfaces suggest the presence of a highly damaged zone around the main crack tip.
CEA-Saclay, Service de Physique de l’Etat Condensé (SPEC), 91191 Gif-sur-Yvette Cedex, France
& ESPCI, UMR Gulliver, EC2M, Bât. H, 10 rue Vauquelin, 75231 Pris Cedex 05, France
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