Thermo-mechanical coupling in electrical penetration assembly: residual strain analysis with embedded FBG strain monitoring

• Residual stress can be effectively released by thermal cycling; after five cycles, the CTE curve stabilizes and peak stress decreases. • Stable compressive residual stress is achieved when Δα > 0 within 8.46–12.73 × 10 −6 K −1 , ensuring reliable sealing. • Small Δα (~1 × 10 −6 K −1 ) enables initial sealing but poor long-term hermeticity; negative Δα causes glass cracking. • Embedded fiber Bragg gratings (FBGs) enable three-dimensional reconstruction of residual strain fields; maximum compression occurs at the glass center. Glass-to-metal (GTM) seals are essential in Electrical Penetration Assemblies (EPAs) of nuclear power plants, where long-term hermeticity relies on residual stress generated by thermal expansion mismatch (Δ α ). However, conventional models cannot capture the thermo-mechanical interactions and uneven residual stress fields that often induce sealing failure, making accurate prediction and monitoring a major challenge. In this study, a thermo-mechanical analytical framework incorporating interface shear–normal stress coupling, finite element modeling, and embedded fiber Bragg grating arrays was combined to achieve real-time three-dimensional strain monitoring during manufacturing and service processes. Results demonstrate that a controlled positive Δ α (8.46–12.73 × 10 −6 K −1 ) yields stable compressive stresses, whereas negative or insufficient Δ α induces cracking or hermetic degradation. Furthermore, thermal cycling experiments revealed progressive residual stress relaxation and structural stabilization of the glass. These findings provide practical guidelines for improving the sealing reliability of nuclear EPAs and offer a transferable methodology for other high-temperature thermo-mechanical structures.