Static fatigue transition in optical glass fibres

Polymer coated optical glass fibres can exhibit under severe environmental conditions, e.g. water at 80°C, an accelerated static fatigue behaviour at long times under moderate stresses. This accelerated fatigue effect depends upon temperature, relative humidity and pH, but even more so on the presence or absence of and type of polymeric coating. To better understand the effect of coatings, a wide variety of coatings (polyurethane acrylate, fluorinated acrylate, polyimide, silicone) on optical glass fibres were tested for their effectiveness in inhibiting this accelerated fatigue behaviour. It was found that the most effective coatings in increasing the resistance of the fibre to accelerated fatigue were phenyl methyl silicone and polyimide. In addition, it was confirmed that the onset of significant strength loss during zero stress ageing occurs at about the same time as the static fatigue transition. Furthermore, the width of the distribution in failure times at a given applied stress decreased significantly after the transition occurs, indicating that these distributions can be used to monitor the onset of the static fatigue transition. Finally, it is shown that this accelerated fatigue behaviour in optical glass fibres can be predicted by assuming that the fatigue transition is due to the effects of stress corrosion and zero stress ageing