Static and Dynamic Fatigue of a Polymer-Coated Fused Silica Optical Fiber

The dependence of fracture strength on tensile strain rate (dynamic fatigue) was used to establish the characteristic slow‐crack‐growth parameters in ethylene vinyl acetate‐coated optical fibers. Strength was measured with five strain rates at each of four relative humidities (from 2 to 97% rh) on specimens 5 cm long. The inert fracture strength was measured at a low temperature in a dry atmosphere. The results of these tests were incorporated into a fracture mechanics model, including slow crack growth, for static fatigue. An increase in relative humidity promotes dynamic fatigue and leads to a predicted acceleration of static fatigue. Measurements of the static fatigue time‐to‐failure at three applied stress levels (on specimens 61 cm long) in 97% rh agree with the predicted behavior based on dynamic fatigue. The applicability of fracture mechanics crack‐growth laws to fused silica fibers is discussed in terms of the Charles and Hillig stress‐corrosion model.