EFFECT OF HUMIDITY ON SMALL-CRACK GROWTH IN SILICA OPTICAL FIBERS

Subcritical small-crack growth in silica optical fibers was measured d irectly in air at 25-degrees-C for several humidity conditions from 30 % to 90% relative humidity. The crack velocity data were shown to be c losely fitted by a power function of the stress intensity factor. It w as found that the power n is independent of humidity and takes a value of 21.7. It was also revealed that crack velocity varies with relativ e humidity to a power of 2.5, which agrees with estimates from the pub lished dynamic fatigue data concerning the humidity dependence of the strength of pristine silica fibers.