| Popis: |
The reliability of long lengths of fibers in optical cables is determined by the presence of weak spots which are infrequently produced by normal fiber production methods. Particles from the atmosphere may cause weak spots on the fiber surface during the drawing process. Abrasive damage of the fiber surface may occur when physically contacting the drawing equipment. Finally, interior weakening of the fiber may occur during preform manufacture because of voids and particles, embedded inside the preform. Four representative types of such flaws have been studied with respect to their mechanical fatigue in normal atmosphere, 23 degree(s)C, and 50% relative humidity. The results are summarized in this paper. Fatigue of zirconia induced weak spots was observed in rapid tests, being significantly less or absent, at lower stress rates. No fatigue was observed in fiber with particles of chromium oxide deeply embedded in the glass. The effect of the size of particles was also studied, by comparing tensile test results with a theoretical strength distribution, based on an assumed relation between particle size and fiber strength. The size of particles appeared to have no significant influence on the atmospheric fatigue of fiber. A significant time-dependence of strength was found in weak spots caused by physical contact with glass during drawing. The static fatigue is apparently the same as for flaw-free fiber. No fatigue was found of weak spots originating from abrasive contact with metal, in the coating die. |
