Intrinsic strength of light guide fibers

The intrinsic strength ((sigma) i) is defined as the strength in the absence of slow crack growth or fatigue. It is of general interest in the study of brittle fracture, but it is of particular importance in the evaluation of lightguide fiber lifetimes since it is required for the calculation of the constant B. In this work we review the existing literature relating to the inert strength, indicate the limits that can be proposed for and suggest possible approaches to more satisfactory estimates of value(s) of (sigma) i. It is suggested that reasonable values of the inert strength may be obtained by taking 85 - 90% of the liquid nitrogen strength.