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Abstract: The strain dependence of critical current I c of a commercial RABiTS (Rolling-Assisted Biaxially Textured Substrates) YBCO coated conductor tape with Cu stabilizing layers on both surfaces has been studied by two kinds of bending apparatus and a tensile apparatus at 77K and 293K. According to the voltage measurements using multi-taps in the longitudinal direction, local I c degradation was also observed. In the continuous bending-tension test at 77K, in which YBCO layer was subjected to the tensile strain, I c began to decrease rapidly beyond the strain of 0.6% after initial moderate degradation. In the continuous bending-compression tests, the I c began to decrease rapidly beyond the strain of 0.4%. The strain for the beginning of degradation of I c obtained by tensile tests at 77K was almost the same as that by the bending-tension tests. Bending test at RT using FRP holders showed I c degradation not so different from that by the continuous bending tests at 77K. In all tests, the I c initially degraded locally irrespective of the position in the specimens. Furthermore, I c degradation by repeated bending was also studied. [Copyright &y& Elsevier]

It was reported that Lorentz force caused degradation of critical current in the ITER-TFMC conductor. We have used our novel experimental setup, which utilizes the closed electric circuit concept for critical current and stability measurements of multi-stand superconducting cables. The feature of this setup is mechanical loading applied to the multi-strand cable in the transverse direction. Significant degradation in the critical current of the cable was observed when the average compressive stress was about 20 MPa. This degradation was found irreversible after unloading. We tested the cable with epoxy or ice molds as well. No degradation was observed in the molded cables. We also tested the cable with smaller void fraction. In this case, significant degradation in critical current was observed. [ABSTRACT FROM AUTHOR]

We developed a novel critical current and stability experimental setup utilizing a closed electric circuit with a multi-stand superconducting cable. The feature of this setup is transverse mechanical loading implied to the multi-strand cable in the transverse direction. It was reported that Lorentz force caused degradation of critical current in the ITER-TFMC conductor. Furthermore, these phenomena were only observed in the ITER full size conductors with large Lorentz forces under high magnetic field. The advantage of our setup is a critical current measurement with comparable mechanical stress under high magnetic field. Employing an inductive critical current measurement technique, we conducted the experiment with transport current of around 10 kA without any power supply nor current lead. As experimental results, we observed significant degradation due to compressive stress of around 30 MPa. This degradation was found irreversible, when it was unloaded. [ABSTRACT FROM AUTHOR]

Abstract: In order to supplement the VAMAS round robin test (RRT) on the bending strain dependence of critical current, I c, of Ag/Bi-2223 tapes conducted in 2001, a miniature bending RRT at 77K and room temperature, RT, participated by three laboratories has been conducted. Three devices developed by Goldacker of Karlsruhe, which allow continuous change of the bending radius of the sample and measurements of I c at 77K have been used. The onset strains for steep I c degradation, ε irr , at 77K, 0.55%, was larger than that at RT, 0.37%. This is due to an additional pre-compression in Bi-2223 filaments for the bending at 77K. The comparison of the present results bent at RT with those in the VAMAS-RRT showed that the scatters in the degradation behaviors were substantially small in the present results. ε irr of the former was larger than that of the latter. These appear to be explained by the different thermal histories. Based on the results, some attempts to reduce the scatter of bending test results were tried. [Copyright &y& Elsevier]

Bending strain dependence of critical current, Ic, of Ag/Bi-2223 57 filament tapes was investigated at 77 K and room temperature, RT, using a device invented by Goldacker. The strain where Ic start to degrade steeply at 77 K, 0.48%, was larger than that at RT, 0.36%. This is an indication of an additional pre-compression in filaments to be bent at 77 K compared with that at RT. According to the voltage measurements using multiple taps in the longitudinal direction, the Ic degradation behaviors at both temperatures varied depending on the section in the tape, due presumably to the difference in the crack propagation characteristics associated with the non-uniformity of the micro-structure. The onset strain for Ic degradation was more precisely determined. The degradation characteristics were shifted to the smaller strain in the present result as compared with that obtained by bending tests using G10 sample holders of different bending radius. The difference can be explained by the different thermal history on setting specimens to the holder and the constraints during cooling. The repeated bending tests at 77 K showed that the discrimination between the gradual and steep degradation stages was clear and the degradation was controlled by both the maximum strain and the strain range. [Copyright &y& Elsevier]