Monitoring fatigue failure in REBCO coated conductors at cryogenic temperatures using advanced optical fiber sensors

Abstract Fatigue failure from cyclic loading, such as thermal cycles and electromagnetic forces, poses a significant challenge for rare-earth barium copper oxide (REBCO) coated conductor (CC) tape. Addressing this issue requires effective real-time evaluation techniques to enhance our understanding of fatigue properties and predict potential failures. A new method has been developed to detect and locate fatigue damage by reconstructing time-series macro-strain data using Rayleigh scattering-based optical frequency-domain reflectometry distributed optical fiber sensors (DOFSs). These newly developed copper-coated sensors are installed on the surface of REBCO tape, achieving perfect fit and consistency with the deformation of the tape. The strain measurements obtained from welded-DOFS and bonded-DOFS, which used epoxy resin at liquid nitrogen temperature, were compared. A series of cyclic tests at this temperature differentiated mechanical and thermal fatigue using welded-DOFS. A theoretical model for fatigue damage in REBCO, based on accumulated maximum strain data, was established, explaining how mechanical parameters and temperature changes affect fatigue properties. Experimental results show that welded-DOFS outperforms bonded-DOFS under cyclic loading at liquid nitrogen temperature. This provides a reliable measurement method for distinguishing mechanical and thermal fatigue, detecting, localizing damage, predicting fractures and remaining life in REBCO CC tapes.