Resin Directional Flow and Degree of Cure Sensing Using Chirped Optical Fiber Long Period Gratings

Abstract

The use of chirped long period gratings (CLPGs) for monitoring the flow, the direction of the flow and the subsequent cure of an epoxy resin is presented. The asymmetric properties of the CLPG and its sensitivity to refractive index changes were exploited to facilitate the measurement of the direction of the flow. The performances of a continuously chirped LPG (CCLPG) and a step chirped LPG (SCLPG) were compared, with the CCLPG showing improved spatial resolution. The CCLPG and SCLPG were also used to monitor changes in the refractive index of the resin during cure, with the results showing close agreement with measurements undertaken simultaneously using a fibre optic Fresnel refractometer.

Production process monitoring and post-production strain measurement on a full-size carbon-fibre composite aircraft tail cone assembly using embedded optical fibre sensors

“…Optical fibre interferometers, such as the extrinsic Fabry-Perot interferometer, have been used to monitor the development of internal strains during the curing of a composite [20]. The infusion, flow and cure of resin can also be monitored using optical fibre grating sensors such as fibre Bragg grating (FBG), tilted fibre Bragg grating (TFBG) and long period grating (LPG) sensors [10,[21][22][23][24][25]. Grating sensors can be configured to perform multi-parameter sensing, which is useful for the simultaneous measurement of strain and temperature [26][27][28][29].…”