ANALYTICAL MODELING OF THE INTERFACIAL SHEARING STRESS IN DUAL-COATEDOPTICAL-FIBER SPECIMENS SUBJECTED TO TENSION

A simple analytical model is developed for the evaluation of interfaci al shearing stress at the glass fiber surface in dual-coated optical f iber specimens subjected to tension. The analysis has been performed f or pull-out testing and in situ evaluation of Young's (shear) modulus of the primary coating material and is aimed at assessment of the effe ct of the materials properties and the specimen's geometry on the magn itude and distribution of interfacial shearing stress. It is shown tha t the longitudinal distribution of this stress is nonuniform and that, for the given specimen's length, its maximum value increases with a d ecrease in the thickness of the primary coating. It is concluded that, while currently used 1-cm-long specimens with approximately 30-mum-th ick 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 pri mary coating material in fibers of different lengths and with differen t coating designs, as well as for the evaluation of Young's (shear) mo dulus of this material from the measured axial displacement of the gla ss fiber.