Abstract Body

The second-generation high-temperature superconducting (2G-HTS) tapes are subjected to complex stress/strain in practical applications. For the complex operation conditions, lamination techniques are widely used to improve the robustness of tapes. However, lamination makes the 2G-HTS tape structure more complicated, which can significantly affect their electro-mechanical behaviors. In this work, uniaxial monotonic tensile tests were performed to obtain the stress-strain relationship and the strain dependence of critical current (I_c(ε)) in liquid nitrogen conditions. Two types of laminated 2G-HTS tapes (copper-laminated and stainless steel-laminated) were compared with copper-plated 2G-HTS tapes. The results showed that the irreversible tensile strains of Cu-laminated and SS-laminated tapes were much higher than that of Cu-plated tapes, which increased by ~35% and ~60%, respectively. High consistency between the experimental and theoretical I_c values in 2G-HTS tapes under tensile strain was verified by the I_c(ε) model. Based on the residual strain (ε_res) calculation of composite multilayer structures, we confirmed that it was mainly due to the increase of the compressive residual strain of superconducting layers. Further, tensile fatigue tests also confirmed the significant improvement of the tensile fatigue electro-mechanical behaviors in the laminated 2G-HTS tapes. Finally, 2D X-ray and SEM cooperative analysis were used to characterize the tape microstructure before and after fatigue, and the correlation between micro-defects and non-destructive imaging features was established. It was found that the internal solder layer and its interface were seriously damaged to release the stress.

This work provides a strategy to improve the electro-mechanical behaviors of 2G-HTS tapes by adjusting the composite structure to change residual strain.

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Acknowledgment

This work was financially supported by the National Key R&D Program of China of National Natural Science Foundation of China (Grant No. 2022YFE03150201), the National Natural Science Foundation of China (Grant No.52277027), and Scientific Research Program of Science and Technology commission of Shanghai Municipality (Grant No. 21XD1430700). The authors would like to acknowledge the instrumental analysis center (IAC) of Shanghai Jiao Tong University for specimen preparation and structural characterization.