Fatigue Behavior of Y–Ba–Cu–O/Hastelloy-C Coated Conductor at 77 K

Abstract

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 YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-delta</sub> /Hastelloy-C coated conductors. The effects of longitudinal tensile fatigue on the critical current and the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -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 xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> degradation in fatigued samples. Further, the fatigue strength and ductility behaviors analyzed using a 5% reduction in <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> 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.