Strength increase of fibers after aging under load

One major risk in the employment of fiber optic cables in telecommunications applications is the possibility of mechanical failure of the fibers after several years under moderate static loads. Present data do not sufficiently discriminate among possible fatigue models to allow us to make absolute lifetime predictions for useful time periods on the order of 20 years or more.1 However, by applying compressive strengthening to glass fibers, one can establish a fatigue limit for the fibers greater than the expected static loads of approximately 20 ksi and guarantee that no failures will occur because of these static loads. We have observed indications of this fatigue limit for compressively strengthened optical fibers and have even observed significant strength improvement of severely damaged fibers aged under loads less than but nearly equal to the magnitude of the compressive strengthening.