Fracture toughness of fused SiO sub 2 and float glass at elevated temperatures

The fracture toughnesses of fused SiO sub 2 and float glass were measured at high temps. In both glasses, low-temp. regions of elastic fracture were identified and correlated with the elastic moduli and their temp. dependence. A viscous flow contribution to fracture toughness was identified in the fused SiO sub 2 at T greater than 800 degrees C. Similar indications of viscous flow were also noted in the float glass, although at much lower temps.