Measurement of the silica glass fatigue limit

The static fatigue limit, or the threshold stress intensity factor, K o , for first subcritical crack growth has been measured directly in silica glass for T  ≥ 600°C using the double cantilever beam (DCB) crack growth technique. Values measured ranged from 0.48 to 0.61 MPa·m 1/2 for a temperature range of 600°C‐850°C, respectively. Cracks growing near the static fatigue limit had a time‐dependence, where the crack growth decreased and appeared to stop at K  ≈  K o . Slow crack growth curves ( K ‐ v ) have been measured from room temperature, 50% RH, up to 850°C with subcritical crack growth not measurable for T > 900°C. Increasing temperature was found to first increase, and then decrease the slope of Region I, and a peak in fatigue resistance was found around 150°C‐300°C. At T > 600°C subcritical crack growth was observed for K higher than previously measured K IC values. This observation and the static fatigue limit in silica are explained by a water‐assisted stress relaxation mechanism at the crack tip.