Adhesively Bonded Optical Sensors: Stress Transfer and Durability

摘要

In this study, adhesively bonded optical fibers and Bragg grating sensors were investigated. The primary objectives were to assess the durability of the optical fiber-to-composite bond during loading and how that load was transferred from the structure to the optical fiber sensor. Using a two-phase epoxy and a highly reproducible bonding technique, different specimen configurations were fabricated and tested under cyclic fatigue loading. The parameters that were considered were the orientation of the top ply of the composite and the loading direction relative to the optical fiber. In addition, the load transfer from the structural composite to the optical sensor was studied numerically and experimentally. In all the specimen configurations studied, cyclic fatigue to 0.3% strain did not lead to cracking of the bond up to 500,000 cycles. The bonded sensor performance was unchanged during these experiments. A bonded optical sensor was proven functional up to 0.55% strain, where the composite failed. The top ply orientation of the laminate relative to the optical fiber did not seem to have a significant effect, although the stress analysis showed that the stresses in the adhesive and the part of the fiber nearest to the substrate did vary significantly. The stress analysis further indicated that loading transverse to the bonded optical fiber should be most critical in terms of bond durability. The analysis showed that strain is primarily transferred along the fiber axis, not in the transverse direction. Thus, the strain state in the bonded fiber may be approximated to that in an axially loaded free fiber.