Electric field-assisted embedding of fiber optic sensors in structural materials for structural health monitoring

Embedding fiber optic sensors in critical components is a key step for real-time monitoring of structural conditions during service and supporting autonomous system operations. Successful integration of these sensors necessitates effective interfacial bonding between the fiber and matrix, good integrity and functionality of the embedded sensors, robust mechanical strength of the matrix materials, and the ability to retain these properties during transient thermal and stress events. This study demonstrates the encapsulation of fused silica optical fibers in stainless steel and nickel through the electric field-assisted sintering (EFAS) process. Copper-coated and gold-coated single mode optical fibers were embedded under different EFAS conditions. The resulting components with embedded sensors were evaluated using advanced microscopy and optical frequency domain reflectometry (OFDR) to assess the aforementioned critical aspects of embedding. The results indicate that both copper- and gold-coated fibers can be successfully embedded in stainless steel and nickel with good fiber integrity and fiber-matrix bonding. Samples fabricated under optimal conditions passed helium leak testing, confirming effective interfacial bonding. Microstructural characterization revealed excellent fiber-matrix adhesion and interdiffusion of elements across the interface. The functionality of the embedded fibers was evaluated through OFDR scans, which revealed signal insertion loss of 0.43 – 0.52 dB for nickel samples and 0 – 0.75 dB for stainless steel samples at the embedding sites. Additionally, the embedded fibers underwent cyclic thermal treatment between 500°C and 700°C. The fibers maintained good integrity and interfacial characteristics, demonstrating their ability to survive cyclic thermal events for sensing in harsh environments.