Threshold Stress Intensity Factor In Soda-Lime Silicate Glass By Interrupted Static Fatigue Test

The measurement of the threshold stress intensity factor Kth for sub-critical crack growth of soda-lime glass in a water environment was performed using the interrupted static fatigue test. The experimental procedures suggested in a previous paper by the current authors were followed. In the first approach, Kth was calculated as the stress intensity factor at which half of the specimens fail during the constant stress phase of the test. In the second approach, the fatigue limit was determined from the stress intensity factor applied to the weakest surviving sample during the stress hold. For both cases, values of the stress intensity factor were obtained for increasing hold times, which ranged from 1 hour to 20 days. The estimated Kth values decrease with holding time but are expected to reach a limiting value, equivalent to the true threshold at long times. For holding times of 20 days, values of 0.16 and 0.15 MPa m1/2 were obtained by using the two different approaches. For the current test, the necessary limit in the estimated Kth values was not obtained, suggesting that if a threshold exists, it must be equal to or less than these values. These values are significantly lower than previous Kth estimates that were obtained by extrapolation from crack velocity and time-to-failure measurements (0.2-0.4 MPa m1/2).