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28 September 1994 Dependence of fiber strength on time, temperature, and relative humidity
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The most critical variable effecting the strength of silica lightguides is the availability of water to the fiber surface. At very low temperatures (T < 77 °K) and at high vacuum (PH2O < i07 torr) the thermodynamic activity of water is so low that mechanical failure of the fiber occurs by the direct breaking of Si-O-Si bonds. In this case very high strength (- 12-14 GPa) and very slight time dependence (formula available in paper) are expected. Also an activation energy comparable to the SiO bond energy is observed (- 100 kcals/mol). On the other hand, under normal conditions (T - 0- 100°C and normal relative humidity), the strength and time dependence are controlled by the combination of stress and the reactivity of water with the fiber surface: SiO2 + H2O = SiOH HOSi. In this case the time dependence of strength is very much greater (n 20) and the activation energy is approximately 30 kcaI/mol.2 Because of this rather extreme time dependence, the short time tensile strength (say tf = 10 sees) is only about 5.5 GPa and will be reduced again by a factor of 2 (to = 2.8 GPa) in about one week. A subject which continues to be discussed and studied is the proper analytical description of this time dependence. In this regard, Bubel and Matthewson3 have studied the behavior of several proposed models for time dependence. They find that the differences in predicted lifetimes from the models differs significantly. In particular they suggest that the universal use of the optimistic power law is not appropriate.
© (1994) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Charles R. Kurkjian, Daryl Inniss, M. John Matthewson, and P. K. Gupta "Dependence of fiber strength on time, temperature, and relative humidity", Proc. SPIE 2290, Fiber Optic Materials and Components, (28 September 1994);


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