Application of fracture-mechanics theory to fatigue failure of optical glass fibers

Abstract

The fatigue behavior of optical glass fibers was determined in air at 23°C and 55% relative humidity by the dynamic-fatigue test technique in which strength is measured as a function of stressing rate. The good correlation found between the fatigue test data and fracture-mechanics theory indicates that failure is controlled by slow crack growth of preexisting flaws and that fracture-mechanics theory can be used in making failure predictions for optical glass fibers.

Thermal activation effects in crack propagation and reliability of fused silica

“…Other observations were similar to these, or reported the increased ratio of observed velocities as a function of increased temperature . Supporting evidence for thermally activated increases in crack velocity with temperature in fused silica is provided by decreased failure times in the constant stress failure data of Figure C 35 and earlier and decreased strengths in constant stressing rate data …”

Subthreshold flaws and their failure prediction in long-distance optical fiber cables

“…These values are needed to make the prediction. It is shown in Appendix A that the probability of a failure F, in a length L , having survived a proof stress U,,, is F, = I -exp (Lu,"(uj; -(s/t,,)''l'")) (4) where S = E ( u " t ) for all applied stresses U for time t experienced by the length L, including the prooftest, and the fatigue constant n is derived empirically. This result is equivalent to that of [21], but is here derived with minimal dependence on fatigue theory, making use instead of empirical data and the equivalence of the fatigue processes in the field and in the prooftest.…”

“…[2]- [4], cannot be applied to typical flaws in optical fibers. Somewhat fortuitously, the widespread use of this description in currently proposed prediction methods, coupled with natural conservatism in design, appears to have resulted in substantial safety margins being applied in practice, as indicated by the apparent lack of unexpected failures in the field.…”

Environmental Fatigue of Silicate Glasses in Humid Conditions

“…This equation allows direct comparison between slow crack growth studies and dynamic fatigue studies. The fatigue of glass has been studied using different strength measurements, including tensile tests, two‐point bending (TPB) tests, three‐point bending tests, four‐point bending tests, and ring‐on‐ring tests …”

“…This equation allows direct comparison between slow crack growth studies and dynamic fatigue studies. The fatigue of glass has been studied using different strength measurements, including tensile tests, [15][16][17][18][19] two-point bending (TPB) tests, [20][21][22][23] three-point bending tests, 3,24 fourpoint bending tests, 25,26 and ring-on-ring tests. 27 Even though the fatigue parameters for slow crack growth and strength measurements are equivalent, differences in the value of n for the same materials (silica glass) have been reported.…”