Thermomechanical Mechanism for Delamination of Polymer Coatings From Optical Fibers

Abstract

Sometimes the polymer coating on an optical fiber is observed to have separated from the fiber over a small portion of the interface. Irregularities on the capstans and sheaves of draw, rewind, coloring, and cabling machines can initiate such delaminations. Subsequent growth would not be anticipated under the condition of radial compressive stress that might be expected for a coating shrinking over a relatively rigid fiber as the composite cools during manufacture. Compressive stress is indeed found at the interface when a single-layer coating is used. However, for a two-layer system, having a high-modulus secondary over a low-modulus primary (for improved protection against microbending), the different rates of thermal expansion can lead to radial tension at the silica/primary interface, and this tension can “drive” the growth of delaminations. A principal result of this study is that the analysis predicts the primary coating, although rubbery, to be approximately in a state of uniform hydrostatic tension. This tensile stress is of substantial magnitude because of constraints imposed by the relatively stiff secondary coating and by the fiber. The existence of significant radial tension at the fiber surface is consistent with experimental observations of induced delaminations, which are seen to grow long after cessation of external disturbances.

Fiber Optics Structural Mechanics: Brief Review

“…Polymerically coated (Devadoss, 1992;Gebizioglu and Plitz, 1991) or metallized fibers are widely employed for better short and long-term reliability of the silica material that is both brittle and moisture sensitive. Problems encountered during design, manufacturing, testing, and reliability assessments of dual-coated glass fibers include: evaluation of the effect of coating on the bending stresses (Suhir, 1988(Suhir, , 1993a(Suhir, , 1997a, understanding the delamination mechanisms and improving strippability (King and Aloisio, 1997;Suhir, 1994), prediction of the magnitude and distribution of stresses occurring during proof (pull-out) testing (Suhir, 1993b(Suhir, , c, d, 1994, and other structural problems.…”

Long-term thermally interfacial-shear-stress-induced delamination of polymeric coatings from glass fibers in double-coated optical fibers

“…Compressive and tensile interfacial normal stresses induce microbending loss in the glass fiber and delamination of the coating, respectively, so both have been extensively studied. [3][4][5][6][7] Thermal shear stress also exists at the interface between the glass fiber and the primary coating. If this interfacial stress exceeds the adhesive strength, the polymeric coatings will be delaminated from the glass fibers and the optical fiber will thus lose its mechanical strength.…”

Thermal stress in a polymer-coated optical glass fiber with a low-modulus coating at the ends

“…Polymer coatings are widely used in fiber optics [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] for better short-and long-term reliability of the silica material, which is both brittle and moisture sensitive. Numerous structural analyses (stress-strain) related problems have been encountered and addressed during design, manufacturing, and testing of coated fibers.…”

“…Numerous structural analyses (stress-strain) related problems have been encountered and addressed during design, manufacturing, and testing of coated fibers. Examples of such problems are: evaluation of the effect of the coating on the bending stress in fibers; understanding the delamination mechanisms, and improving both the interfacial strength and strippability 9,10 ; prediction of the stresses and curvatures occurring during the lowtemperature microbending or proof (pull-out) testing of coated fibers 11-16 ; etc. In the analysis that follows, a polymer-coated fiber with a low modulus coating at the ends ( Fig. 1) is considered.…”