Temperature dependence of strength and fatigue of fused silica fiber in the range 77 to 473 K

Abstract

The strength of optical fiber at low temperature is an important parameter since it approximates the inert strength, i. e. the starting strength of the material before degradation by fatigue. Published data suggest that the fatigue may abruptly slow below some temperature. However, published data are limited to strength vs temperature or fatigue in liquid nitrogen. We report strength and fatigue data for both bare (stripped) and metal coated fused silica optical fiber at temperatures down to 77 K. While fatigue slows as the temperature is reduced (i.e. the stress corrosion parameter increases with falling temperature) fatigue is still measurable at 77 K. This is the case even for hermetic metal coated fiber with extremely low water activity at the glass surface. The results confirm that fused silica exhibits "intrinsic" fatigue, i.e. fatigue in the absence of moisture.

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 …”

“…36 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 2C 35 and earlier 37,38 and decreased strengths in constant stressing rate data. [38][39][40][41][42] For each experimental data collection such as in Figure 3, a single value of G within the domain of exponential behavior was selected and the v(T) behavior determined. For each distinct v i (T i ), v j (T j ) pair within a collection, Equation (8) was then used to estimate a value of u 1 using the value of G selected and the a and 2γ values determined above.…”