Approximate evaluation of the interfacial shearing stress in cylindrical double lap shear joints with application to dual-coated optical fibers

Abstract

A simplified 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, in situ measurements of Young's (shear) modulus of the primary coating material, and stripping of the coating from the glass. The objective of the analysis is to assess the effect of the material properties and specimen's geometry on the magnitude and distribution of 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. As far as the pull-out testing and Young's modulus evaluations are concerned, it is concluded that, while 1 cm long specimens with approximately 30 μm thick primary coating (such specimens are currently used in pull-out tests) are acceptable, shorter specimens will result in a more uniform stress distribution and, as a consequence of that, in more stable experimental data. As to the coating strippability, it is desirable that the stripping area be short, although satisfactory strippability is often achieved even for long stripping areas. It is concluded that a multiblade stripping tool might be worthwhile to consider if long portions of coating have to be removed from the fiber.The obtained results can be useful for comparing the adhesive strength of the primary coating in fibers of different lengths 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, and for the assessment of the effect of material properties and fiber geometry on the strippability of the fiber coating.