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 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.

Effects of room-temperature tensile fatigue on critical current andn-value of IBAD–MOCVD YBa2Cu3O7−x/Hastelloy coated conductor

“…Comparing these results to those from Mbaruku et al [19], here we find that for ε=0.35% 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 cycles. This may be due to differences in the fatigue ratio.…”

“…For ε=0.45%, Mbaruku et al [19] showed that conductor damage occurs at 1,000 cycles whereas in this work I c reduction did not occur until 10,000 cycles. Improvements in the manufacturing processes may explain the increased strain tolerance at elevated ε and low N. These improvements are overshadowed at high N by the increased strain energy using a loading path with R=0.…”

“…Mbaruku et al [19] showed that the mechanical properties of REBCO conductor are driven primarily by those of the Hastelloy substrate. It is important to note that the REBCO conductor is a composite system, and failure within any of the conductor layers can trigger electrical The SEM images of the as-received conductor show microcracks along the conductor edge, which are likely due to the slitting process used to convert the 12 mm wide as-grown conductor into three 4 mm wide conductors.…”

Delamination behaviors of GdBCO CC tapes under different transverse loading conditions

“…This stress /strain induced by mismatch of the coefficient of thermal expansion among each constituent layers present on the CC tape causes the degradation of its electromechanical properties particularly the critical current (I c ) through the occurrence of delamination. Furthermore, in some device applications, by repeated loading due to rotational stresses, applications that utilize alternating current, random loads and mobile system, and thermal cycling (repetitive cool down and removal from cryogen), might worsen this delamination issue [1]. As reported elsewhere, the I c of an epoxy impregnated double pancake coil degraded due to at almost 5 thermal cycles [2].…”

Progresses and challenges in the development of high-field solenoidal magnets based on RE123 coated conductors

“…High stresses have higher probabilities to quickly damage the ceramic compound, whereas large fatigue stress ratio can slowly generate cracks in the metals of the composite tape. Mbaruku et al [69] were the first to characterize commercial CCs in cycles >100k. In particular, their work has pointed out that fatigue cracks in the RE123 layer do not occur everywhere in the sample but are localized in weak areas, starting from the sample edge and moving towards the center (likely due to the slitting process used to cut a 12 mm wide tape into three strips of 4 mm width).…”