Effects of OH content, water vapor pressure, and temperature on sub-critical crack growth in phosphate glass

The effects of temperature and water vapor pressure on the rate of sub-crit ical crack growth in meta-phosphate laser glasses containing different OH c oncentrations (128 and 773 ppmw) are reported. The crack velocity was measu red using the double-cleavage-drilled-compression method. When plotted as a function of stress intensity, the samples have the classic region I, II an d III crack growth properties similar to that reported for silicate glasses . The glass containing the larger OH content has a 10-fold greater crack ve locity in region I; crack velocities is region II are the nearly the same f or both glasses. The crack velocities are analyzed using a chemical kinetic and mass-transport limited reaction rate model. At temperatures >150 degre es C and water vapor pressures >10 mmHg, crack tip blunting is observed and the glass containing the larger OH content is more prone to blunting. (C) 2000 Published by Elsevier Science B.V. All rights reserved.