Interfacial shearing stress in a cylindrical double lap shear joint, with application to dual-coated optical fiber specimens

A simple analytical model is developed for the evaluation of the interfacial shearing stress in a cylindrical double lap shear joint, with application to dual-coated optical fiber specimens subjected to pull-out testing and in-situ measurements of Young´s (shear) modulus of the primary coating material. The purpose of the analysis is to assess the effect of the materials properties and specimen´s geometry on the 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 1 cm long specimens with approximately 30 μm thick primary coating (these are currently used as pull-out test specimens) are acceptable, shorter specimens will result in a more uniform stress distribution, and, as a consequence of that, in more stable experimental data. The obtained results can be useful for comparing the adhesive strength of the primary coating in fibers of different length and with different coating designs, for the in-situ evaluation of Young´s modulus of the primary coating material from the measured axial displacement of the glass fiber