IN-SITU STRAIN MONITORING OF 3-D WOVENCOMPOSITES USING INTEGRATED FIBER OPTIC SENSORS

摘要

The goal of this work was to demonstrate monitoring of internal strains using fiber optic sensorsintegrated within the reinforcement of 3-D woven composites. The unique feature of the project was thatoptical sensors were woven in as the preform was fabricated, allowing the sensors to nest intimatelywithin the tows, including tows in through-thickness direction. Addressed herein are the 4-point bendingand lap-shear testing of 3-D woven composite specimens with woven-in sensors, procedures used forstrain monitoring, and comparison of the results with data from foils gage used for reference. The opticalsensors measured strains in X, Y, and Z axes which correlate with data from foil gages. Optic sensor datawas then used to determine the in-plane and through-thickness shear moduli for the 3-D woven fabriccomposite. A sensor located near an open hole detected elevated strains. Sensors near the "step" in theshear sample captured the nonlinear load-strain responses, as did foil gages mounted on the samplesurface. Sensors located near/within fiber tows recorded “stiffer” responses, as expected, compared to foilgages overlapping several unit cells. Also discussed are some additional capabilities this new approachprovides and why some difference in strains monitored by fiber optic sensors and foil gages may be seen.