3-D Woven Composites Instrumented With EFPI Fiber Optic Sensors

A novel approach to continuous health monitoring of polymeric composite materials and structural elements using embedded Extrinsic Fabry-Perot Interferometers (EFPI) is proposed and validated. The proof of concept includes several consecutive steps. First, it is verified that simple optical wave guides survived a regular 3-D weaving process. Then EFPI sensor assemblies are manually incorporated into the preforms and it is verified that they are functional. Next step is resin infusion of instrumented preforms using VARTM method, followed by investigation of possible mechanical damage to sensor leads. Finally, test specimens are fabricated, and four-point bending tests are performed. The internal strain monitoring results provided by the embedded fiber optic sensors are compared to the data from surface foil gages. The developed approach validates, particularly, the possibility of continuous through-thickness strain monitoring, which is crucial for composite bonded and bolted joints, components with holes, openings, stiffeners, and other cases of high strain gradients.