Entry of molecular water in the silica glass crack tip during slow crack growth

The mechanical strength of oxide glasses is known to decrease with time under tensile loads in the presence of liquid water or water vapor. Correspondingly, cracks are observed to grow slowly, or subcritically, in these environments. Various mechanisms describing the effects of water on the mechanical strength of glasses have been proposed, but the evidence for these mechanisms remains unclear. In this work, an ATR-FTIR technique is used to show molecular water (H 2 O) entering in significant quantity at the crack tip in silica glass during subcritical crack growth. For crack growth Regions I and II, the quantity of molecular water uptake decreased with increasing stress intensity and no hydroxyl formation was observed. In Region III, no water uptake or hydroxyl formation were observed. A mechanism explaining this behavior based on water-promoted internal friction (viscoelasticity) is proposed.