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Superconducting materials are subjected to various loading in motors, transformers, generators, and other magnet applications. The loading conditions include bending, tension, compression, and fatigue, and result from coil manufacturing, thermal cycling, quenching, and normal operation. Each of these loading conditions can affect the performance of the superconductor and thus the magnet and system. It is important, therefore, to understand the electromechanical behavior of the superconducting material to optimize the design. Here we report the effects of mechanical fatigue at 77 K on the electrical transport properties of YBa2Cu3O 70 /Hastelloy-C coated conductors. The effects of longitudinal tensile fatigue on the critical current and the n-value are reported. Strain controlled fatigue studies include strains up to 0.495% and strain ratios of 0.2 and 0.5. Scanning electron micrographs of the fatigued conductors are used to identify the sources of failure. Crack formation is believed to be the cause of I c degradation in fatigued samples. Further, the fatigue strength and ductility behaviors analyzed using a 5% reduction in I c as the electrical definition of failure showed that the fatigue strength exponent is within the values found for metals but both the fatigue ductility coefficient and exponent show that the material tested is brittle.

Manufacturing of AgMg sheathed Bi2Sr2CaCu2O8+x superconducting tapes involves multiple processes. Microstructural studies across tape sections have shown that the microstructure is nonuniform across the tape. These nonuniformities are largely due to manufacturing defects, even in well-controlled manufacturing processes. Consequently, the electrical and mechanical properties vary in these different sections. Here, we report results from analyzing the electromechanical properties of AgMg sheathed Bi2Sr2CaCu2O8+x tapes in different sections using a statistical approach. 24 samples were studied at strains of 0%, 0.25%, and 0.349% for a total of 72 samples. The probability of electrical and mechanical failures of the tapes is then analyzed using two- and three-parameter Weibull distributions. It is found that the mechanical failure of these tapes is homogeneous, consistent with failure in the AgMg sheath, but that the electromechanical failure is inhomogeneous within the conductor and as a function of strain, indicating that this failure is dictated by failure in the inhomogeneous ceramic oxide superconducting filaments. This has important implications for the designs of superconducting magnets.