FRACTOGRAPHIC ANALYSIS OF HYDROTHERMALLY TREATED SILICA GLASS

Hydrothermal treatment of abraded silica glass in water produces a sig nificant increase in fracture strength and fracture toughness. This wa s attributed earlier to crack tip blunting. The so-called 'mirror cons tant' of the fracture surface of hydrothermally treated silica glass w as investigated. It was found that mirror size changed while the crack length remained unchanged with hydrothermal treatment. At the same ti me, the 'mirror constant' increased with hydrothermal treatment. The v ariation of 'mirror constant' was analogous to that of the apparent fr acture toughness value due to crack tip blunting.