Model of effect of environmental attack on flaw growth kinetics of glass

The time rate of extension of a single slit-like flaw in glass is modeled assuming the same corrosion mechanism as previously invoked for modeling delayed failure in glass containing a multiplicity of microscopic scratches or flaws. The rate of extension is expressible in terms of the stress intensity K and is in good agreement with the experimental results reported by Wiederhorn and Bolz and others. The model considers a moisture-induced corrosive attack occurring on the exposed flaw surfaces to be governed by local chemical kinetic and thermodynamic considerations, producing a rounding of the flaw tip. This mechanism accounts for the possibility of threshold behavior. The remotely applied stress becomes magnified as shown by Inglis to require the combined effect of the flaw length and tip curvature. These geometric factors in combination with the remotely applied stress mutually interact through the corrosion kinetics to define the net rate of flaw extension.