Damage in silica by hydroxyl generation : Behaviour at crack tips

Water diffusion into silica glass results in a zone where the water reacts with the SiO₂ structure and "damages" the originally intact SiO₂ rings. The consequence is a reduced Young’s module. This effect must be strongly stress-enhanced at crack tips under the high near-tip stresses. In this report the general influence on crack stability and local failure condition is addressed. The results give rise for subcritical crack growth in the sense of crack extension under applied stress intensity factors below the fracture toughness K$_{Ic}$. A threshold stress intensity factor for subcritical crack growth in silica can be concluded.