Strength evolution of optical fiber submitted to static stress

The strength of silica optical fiber is closely related to the activity of water at its surface. However, observations have shown that the polymeric coating is also a key factor contributing to the mechanical properties of the fiber. While the main role of the coating is to inhibit crack growth from the surface Griffith flaws, it also reduces the water concentration at the glass surface through diffusion processes. Dynamic and static mechanical tests were implemented using a tensile test bench and a static fatigue test under uniform curve. The incidence of aging treatments at 65°C and 85°C was investigated on two standard silica optical fibers (with polyacrylate and fluorinated coatings). Fatigue under static tension was also investigated using a vertical static tensile bench. Microscopic observations helped the understanding of the failure mechanism. It appears that the cyclic variations of the failure stress phenomenon, with respect to the aging time, are the result of the silicate gel which migrates towards the polymer coating.