Stress corrosion in silica may end the lifetime of optical fibers in telecom networks. Since the lifetime demanded usually exceeds 25 years, a careful strategy is necessary in order to preserve cable reliability. The toolbox therefore includes equations for estimating lifetime of fibers, some of them related to the so-called B-parameter. The lifetime is proportional to B, but a value specific for the environment andfiber used has turned out to be difficult to achieve.
Among various experimental methods proposed, the mechanical testing at high stress rates is a physically sound way to confirm the B-value of coated fibers, since testing can be made under similar conditions as prevail during network application. Fatigue tests including high-speed tensile tests have been run on coated silica fibers for a long time. Lately, a new high-stress-rate bending method has been investigated, pushing forward the previous experimental limits.
Values of B from tensile- and bending tests are presented, being 0.004 - 0.10 GPa2 s in tension and considerably less in bending, about 0.0007 GPa2s. A study on some acrylate-coated silica fibers including draw-abraded fibers indicates that the B-value also depends on fiber strength.