The effect of water soaking on the strength of silica glass is studied. When silica glass is immersed in warm water and held there for an extended period of time, the strength increases over that of freshly damaged glass. The increase in strength is a consequence of water diffusion into exposed surfaces of the test specimen, which results in swelling of the glass and shielding of cracks present in the surface of the glass.
In our first paper on this subject (Report 19 of this series), we considered swelling effects on the inert strength. In the present report, the strength under subcritical crack growth conditions is studied.
For tests carried out in humid environment at various loading rates, so-called dynamic strength tests, we could show theoretically that the swelling effect cuased by the reaction of water with silica must result in apparently increased crack-growth exponents. This prediction is in good agreement with results from literature.
In our experiments we could show via an evaluation of the crack extension that even in silicone oil environment local subcritical crack growth accurs.