Embedding Fiber Segment Interferometry for Localization of Defects in Composite Structures

ABSTRACT In the area of structural health monitoring (SHM), embedding strain sensors into smart composites is a key strategy for detecting failures arising from overloads and material inhomogeneity. Fiber optic sensors (FOS) offer notable advantages over conventional electrical strain gauges, including low weight, compactness, high sensitivity, multiplexing capability, and immunity to electromagnetic interference. This study presents the first implementation of the recently introduced fiber segment interferometry (FSI) approach for embedded strain‐sensing in composite materials. While most SHM‐related fiber sensors rely on fiber Bragg gratings (FBGs), FSI provides much higher strain resolutions and allows flexible gauge length adaptation. Furthemore, its integral strain measurement improves sensing fidelity in the presence of local strain gradients. This work investigates the influence of different optical fiber coatings on composite properties and evaluates the performance of embedded sensors during mechanical testing. Fibers were aligned parallel to adjacent plies to minimize delamination. Tensile tests were performed on composites containing polyimide‐ and polyacrylate‐coated optical fibers and compared to neat specimens. The capability of FSI to detect and localize damage was examined by introducing controlled notches and comparing FSI strain measurements with digital image correlation (DIC) under cyclic loading. The results demonstrate that embedding FOS with appropriate coatings does not degrade key mechanical properties. FSI provides highly sensitive integrated strain measurements and reliably localizes defect growth inside the structure. In combination with DIC, it enables comprehensive assessment of internal and surface strain fields, while remaining more suitable for real‐world SHM applications.