IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 25, NO. 3, JUNE 2015 6602104 Macroscopic Strain Response of I c Under Magnetic Fields in Differently Stabilized REBCO CC Tapes H. S. Shin, A. Gorospe, A. R. Nisay, M. J. Dedicatoria, K. D. Sim, S. Awaji, and H. Oguro Abstract—Practically, coated conductor (CC) tapes are apt to be exposed to external magnetic fields, hoop stress, and other inevitable stress- and strain-producing factors during fabrication and cool-down and under operating conditions. In addition, the issue on the strain effect on the I c degradation of REBCO CC tapes under magnetic field is not yet completely understood. In this paper, further investigation on the electromechanical response of CC tapes under magnetic field conditions was conducted. Dif- ferently stabilized CC tapes by Cu lamination and by addition of external brass lamination with different substrate materials were investigated. The I c degradation behaviors at respective magnetic field intensity and against uniaxial tensile strain induced were reported. As observed, magnetic field dependence of I c is not affected by macroscopic strain within the reversible strain region. I c degradation behavior with strain was almost constant for all samples from self-field up to 0.5 T. In addition, the macroscopic pinning force and the irreversibility field were calculated and extrapolated, respectively, to investigate the effect of strain. Index Terms—Coated conductor (CC), critical current, GdBCO, magnetic field, strain effect. I. I NTRODUCTION I N PRACTICAL device applications, the evaluation of the mechanical stress and strain response of the critical current I c is one of the most important things to do to ensure the per- formance of the coated conductor (CC) tapes during operations. For magnet or coil applications, the magnetic field dependence of I c is necessary to predict its performance under high external magnetic fields. Mechanical properties and electrical stabil- ity of second generation (2G) CC tapes have been enhanced through copper reinforcing sheets either by solder lamination or by electroplating. Manuscript received August 11, 2014; accepted October 23, 2014. Date of publication November 4, 2014; date of current version February 6, 2015. This work was supported by the National Research Foundation of Korea under Grant NRF-2014-002640, by Brain Korea 21 plus (BK21+) funded by the Ministry of Education, Republic of Korea, and by the Power Generation and Electricity Delivery Program of Korea Institute of Energy Technology Evaluation and Planning under a Grant funded by the Ministry of Trade, Industry, and Energy. H. S. Shin is with the Department of Mechanical Design Engineering, Andong National University, Andong 760-749, Korea (e-mail: hsshin@andong. ac.kr). A. Gorospe, A. R. Nisay, and M. J. Dedicatoria are with the Department of Mechanical Design Engineering, Graduate School, Andong National University, Andong 760-749, Korea (e-mail: alkinggorospe@yahoo.com; armannisay@yahoo.com; mjayen@yahoo.com). K. D. Sim is with the Korea Electrotechnology Research Institute, Changwon 642-120, Korea (e-mail: skedy@keri.re.kr). S. Awaji and H. Oguro are with the High Field Laboratory for Supercon- ducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan (e-mail: awaji@imr.tohoku.ac.jp; h-oguro@imr.tohoku.ac.jp). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TASC.2014.2366721 Recent studies showed that the I c at self-field is affected by strain, however the effect is dependent on the orientation along the a and b axes of the REBCO layer [1], [2]. The intrinsic strain effect on I c considering its orientation with the a and b axes was almost similar in those differently processed CC tapes having similar REBCO superconducting layer [3]. In addition, it is also dominantly governed by both layers of substrate and stabilizer in CC tapes and the strain state in the REBCO film layer was directly controlled by these layers [4], [5]. Under magnetic field, the microstructure of the REBCO layer determined the magnetic field response of I c and differently processed ones showed a different behavior even though they have the same superconducting layer [6]. In this paper, the magnetic field and mechanical response of I c in RCE-DR GdBCO CC tapes with high current capacity was investigated. The strain effect on I c under magnetic field in differently stabilized GdBCO CC tapes was determined. Both the performance characteristics of the CC tapes against applied uniaxial strain and under high magnetic fields were presented. II. EXPERIMENTAL PROCEDURE A. Sample Commercially available CC tapes, manufactured by SuNAM, fabricated by the reactive co-evaporation by deposition and reaction (RCE-DR) process with different substrate materi- als were supplied for the test. Substrate materials adopted were Hastelloy and stainless steel with thickness of ∼65 and ∼100 μm,respectively. Both samples have ∼2-μm-thick GdBCO superconducting film deposited on the buffer layers and a Ag cap layer for protection and Cu-surround stabilized for thermal and mechanical stability. Properties and specifications of the Cu-stabilized and brass-laminated CC tape samples are presented in Table I. B. Electromechanical Property Evaluation Under Magnetic Field The strain response of I c in GdBCO CC tapes under mag- netic field was measured using the Katagiri-type loading fixture at the High Field Laboratory for Superconducting Materials (HFLSM), Institute of Material Research (IMR) in Tohoku University. Uniaxial load was applied to the sample by moving the pull rod actuated by a stepping motor connected in series with the load cell as can be seen in Fig. 1(a). As the pull rod moves, the upper cam pushes the lower cam and consequently its end with the Cu current terminal moves pulling the CC tape sample axially as shown in Fig. 1(b). To monitor the 1051-8223 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.