Analytical modeling of the interfacial shearing stress in dual-coated optical fiber specimens subjected to tension.

A simple analytical model is developed for the evaluation of interfacial shearing stress at the glass fiber surface in dual-coated optical fiber specimens subjected to tension. The analysis has been performed for pull-out testing and in situ evaluation of Young's (shear) modulus of the primary coating material and is aimed at assessment of the effect of the materials properties and the specimen's geometry on the magnitude and distribution of interfacial shearing stress. It is shown that the longitudinal distribution of this stress is nonuniform and that, for the given specimen's length, its maximum value increases with a decrease in the thickness of the primary coating. It is concluded that, while currently used 1-cm-long specimens with approximately 30-µm-thick primary coatings are acceptable, shorter specimens (say, 5 mm long) are expected to result in more stable experimental data. The results obtained can be useful for comparing the adhesive strength of the primary coating material in fibers of different lengths and with different coating designs, as well as for the evaluation of Young's (shear) modulus of this material from the measured axial displacement of the glass fiber.