The Distribution of the Stress Intensity Factor Along the Front of the Growing Crack in an Optical Glass Fiber

The stress intensity factor K₁ along the front edge of a growing small crack in a silica optical fiber was evaluated by 3-D boundary element analysis based on the crack geometry observed during the delayed fracture test. The variation of K₁ was shown to be little along the front of the growing crack. The crack velocity in the direction normal to the crack front was able to be expressed as a power function of K₁ at each position on the crack front. The crack velocity was also shown to be larger at a position closer to the fiber surface for each value of K₁.