DETERMINATION OF CRACK VELOCITY AS A FUNCTION OF STRESS INTENSITY FROM STATIC FATIGUE DATA

The estimation of lifetime of high-strength (greater than or equal to 1 GPa) glass samples with small cracks at low stress levels (less than or equal to 150 MPa) requires a knowledge of the crack velocity, V, a s a function of the stress intensity factor, K, in the range of V valu es lower than the current limit of measurements (about 10(-11) m/s). I t is shown that V(K) data in this range can be obtained directly from static fatigue measurements without assuming a priori any form for V(K ). The method has been applied to the static fatigue data of Proctor, Whitney, and Johnson on silica fibers, and values of V in the range of 10(-11) to 10(-16) m/s (corresponding to K values of 0.35 to 0.20 MPa .m(0.5)) are reported.