- Email: [email protected]
In situ strain measurements of Bi2223 superconducting filaments in multifilamentary Ag-sheathed Bi2223 superconducting tapes
Physica C 411 (2004) 114–119 www.elsevier.com/locate/physc
In situ strain measurements of Bi2223 superconducting filaments in multifilamentary Ag-sheathed Bi2223 superconducting tapes Hiroshi Okuda a,*, Kohei Morishita b, Shojiro Ochiai a, Dan Dokoh b, Motohide Matsui c, Hiroyuki Fujimoto c, Masugu Sato d b
a International Innovation Center, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan Graduate School of Materials Science and Engineering, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501, Japan c Railway Technical Research Institute, 2-8-3 Hikari, Kokubunji, Tokyo 185-8540, Japan d Japan Synchrotron Radiation Research Institute, 1-1 Kohto, Sayo-gun, Hyogo 679-5198, Japan
Received 21 April 2004; received in revised form 11 May 2004; accepted 31 May 2004 Available online 5 August 2004
Abstract In situ strain measurement was made for Bi2223 superconducting filaments in Ag-sheathed Bi2223 composite tapes utilizing synchrotron radiation. The residual strain was 0.05 ± 0.01% in compression. A small deviation from linear relationship between strain of the Bi2223 filaments and the average strain of the sample was found, meaning a decrease in elastic modulus of the filament even below the irreversible strain. 2004 Elsevier B.V. All rights reserved. PACS: 74.72.Hs; 85.25.Kx Keywords: Bi2223 superconducting composites; In situ strain measurement; Synchrotron radiation
1. Introduction Strain state of the Bi2223 filaments in silversheathed Bi2223 superconducting composite tape is very important to understand both the mechan-
*
Corresponding author. Tel.: +81 75 753 5193; fax: +81 75 753 4841. E-mail address: [email protected] (H. Okuda).
ical and the superconducting properties of the material [1–4]. Therefore, there has been several works to estimate the strain inside the composite based on the elastic–plastic mechanical analysis [5–9]. However, these analysis were based on mechanical modeling of the composite structure that required some assumptions concerning geometrical factors and mechanical properties of the constituent materials. Therefore, a direct measurement of strains of the constituent materials in the
0921-4534/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2004.05.019
H. Okuda et al. / Physica C 411 (2004) 114–119
composite under external load is quite important to predict the reliability of the superconducting composites in use. Ten Haken et al. [10] reported an in situ X-ray diffraction measurement of a model monocore Bi2212/Ag tape by Bragg geometry under an axial applied load, and showed that the Bragg peak shift is observed within the axial strain between 0.001 and +0.002. However, since we do not know a precise value of PoissonÕs ratio of the material, a direct measurement of the axial strain is needed for detailed analysis in order to make a full use of the merit of X-ray strain measurements [11]. In the present work, we conducted an in situ strain measurement of Bi2223 filaments in silver-sheathed multifilamentary Bi2223 tapes under tensile load in transmission (Laue) geometry utilizing synchrotron radiation.
2. Experimental The Ag-sheathed Bi2223 multifilamentary composite tape used in the present experiment was supplied by Korea Electrotechnology Research
115
Institute (KERI). The test samples were cut from the as-supplied 30 m role with 4 mm width and 0.31 mm thickness into short strips of 40 mm in length, and fixed in a set of grooved tabs by epoxy adhesive for tensile test pieces. As shown in Fig. 1, the composite tape consists of outer Ag–Mg alloy sheath and inner pure Ag/Bi2223 composite layer with 55 flat filaments of Bi2223. The volume fraction of the Ag alloy sheath, Bi2223 filaments and the pure Ag was 0.28, 0.42, and 0.30, respectively in the present sample. In order to measure strain free Bragg peaks from the filaments, Bi2223 filaments were extracted from the same composite tape by NH4OH/H2O2 solution. In situ strain measurements were carried out at Beamline 46XU of a synchrotron-radiation facility, SPring8, Japan. A small tensile test machine was mounted on a Huber 512.1 Eulerian cradle on a multiaxis diffractometer. The tensile load was applied by pulling up the upper beam by a geared pulsed motor. The load was monitored by a load cell attached directly to the upper beam. A top-view of the optical set-up in the present measurement is illustrated in Fig. 2(a).
Fig. 1. Cross-sectional view of Ag/Bi2223 composite tape used in the present experiment.
Fig. 2. (a) Schematic illustration of the present in situ measurement set-up. (b) Schematic illustration of the sample set in the in situ test machine. Note that the scattering vector is in parallel to the direction of tension.
116
H. Okuda et al. / Physica C 411 (2004) 114–119
A strong X-ray from an undulator was monochromatized into a beam of 22 keV with 0.1 · 0.5 mm2 in size, and introduced to the sample position. The shift of Bragg peak positions by the tensile load was measured in situ. The position of the sample was monitored by two charge-coupled device (CCD) telescopes. The center of the sample in thickness was controlled within 5 lm from the rotation center of the diffractometer for each scan using the CCDs. In the present slit conditions, this corresponds to the error in 2h within 1.5 · 104 degree at Bi2223 220 peak. As shown in Fig. 2(b), the Bragg peaks were measured in transmission geometry with h–2h configuration. Therefore, the direction of scattering vector is always parallel to the direction of tension. The strain measured in the present experiment directly corresponds to the strain in the direction of uniaxial tensile load.
3. Results and discussion The stress–strain curve of the composite tape obtained by a separate ex situ experiment is shown in Fig. 3. The strain was measured by a displacement of the markers attached at the both ends of the sample using CCD camera. The curve has three characteristic regions, and attributed to be [9], (I) the first elastic region where both Bi2223 filaments and Ag alloy sheath deform elastically, (II) the second region where Bi2223 filaments deform elastically and the Ag alloy sheath deforms plastically. In the last region (III), fracture of Bi2223 filaments characterizes a deformation with almost constant tensile stress. From Fig. 3, we chose four stress levels for the present strain analysis, namely, 0, 40, 90 and 140 N as shown by arrows in the figure. 0 and 40 N correspond to the region (I), 90 N the region (II), and 140 N at the end of region (II). In the following, we call the average strain corresponding to the strain in Fig. 3 as Ôtotal strainÕ, in order to distinguish from the strain of constituent components, i.e., the strain of Bi2223 filaments which is evaluated from the Bragg peaks. Fig. 4 shows the (2 0 0) Bi2223 Bragg peaks under applied tensile load. The intensity is normalized with respect to the incident X-ray flux monitor counts. The angle was corrected by the
Fig. 3. Stress–strain curve of the Ag/Bi2223 composite tape at room temperature. The stress levels used in the present experiment are shown by the arrows.
(1 1 1) diffraction peak of NIST standard Si powder painted with a solvent on the tape. The correction was within 2 · 103 degree for each scan. Since Bi2223 filaments have strong texture with their c axis normal to the tape face, clear peaks are observed only for 200 and 220 in the present measurement. The applied load was kept constant during measurement of a set of peaks for Bi2223, Si, and Ag. It is clearly seen that the peak position moves to the lower angle as the tensile load increases. The Bragg peak from extracted fibers, denoted by closed triangle in the figure, lies between the Bragg peaks for 0 and 90 N, almost close to the peak for 40 N. This result suggests that the residual strain of the Bi2223 filament in the as-supplied composite is in compression and should be equivalent to the external load of about 40 N. For more quantitative analysis, the peaks were fitted by using a Gaussian function. For the fitting, only the data larger than 70% of the peak intensity were used. By using the peak position of Bi2223 in the composites and the stress-free Bi2223 peak obtained for extracted fibers, the strain of Bi2223 filaments in the composite tape was calculated by 1 1 1 Da=a ¼ ; 2 sinðh0 Þ 2 sinðhcomp Þ 2 sinðh0 Þ ð1Þ
H. Okuda et al. / Physica C 411 (2004) 114–119
117
Fig. 4. The peak shift of Bi2223 200 under applied tensile load.
where h0 and hcomp are the peak positions of the extracted fibers and that for composites, respectively. The change of 220 Bragg peak under tensile load is shown in Fig. 5. Since the normalized peak intensity is almost the same order of magnitude as those of 200, the tape does not have a strong preferred orientation within the c plane. As seen in the figure, the shift of the peaks for 220 was quite similar to that for 200. Fig. 6 gives the strain in the Bi2223 fiber obtained from Eq. (1), as a function of applied load
Fig. 6. The filament strain obtained from 200 and 220 peak shift, as a function of applied load.
Fig. 5. The peak shift of Bi2223 220 under applied tensile load.
of the composite. The figure shows an almost linear relationship between the strain in the filaments and the applied load, and the strain state of the Bi2223 filaments turns from compressive to tensile when the applied load reaches 40 N, which corresponds to 35 MPa as average stress. The residual strain corresponds to the point where no external load is applied. Although the strains of the filaments obtained from 220 tend to be slightly smaller than that obtained from 200, the residual strains evaluated from the two indices agree well,
118
H. Okuda et al. / Physica C 411 (2004) 114–119
giving eR = 0.05 ± 0.01% as an average over two independent samples and the two indices. When we extrapolate the strain up to the fracture stress of the composite observed in the present experiment, 155 N, the maximum strain in the filaments at the fracture is estimated to be 0.17% in tension. Therefore, the Bi2223 filament has fracture strain close to 0.17%, and the composite has larger fracture strain of 0.22% for Bi2223 filaments because of the compressive residual strain of 0.05% in the Bi2223 filaments. For more detailed analysis, however, the strain of the Bi2223 filaments should be discussed in terms of the average strain of the composite, since the Bi2223 filaments support larger portion of load when the Ag alloy sheath deforms plastically. If the iso-strain condition holds during deformation of the composite, the total strain, the local strain of the Bi2223 filaments, and that of Ag sheath should agree as long as they deform uniformly, irrespective of whether it is elastic or plastic. To examine the point more clearly, the average filament strain is plotted as a function of total strain of the composite, eT, in Fig. 7. A least-square fit of the strain gives a small convex curvature, whose slope is 1.03 at eT = 0 and 0.58 at eT = 0.24%. As suggested above,
the slope should be unity for uniform deformation. Deviation from the linear relationship is observed in Fig. 7 even at a small total strain of 0.13%, which is well below the reported irreversible strain, this deviation suggests that we need to take the effect of microscopic defect in the Bi2223 filament in the region (II) into account. Therefore, we may safely conclude that effective elastic modulus of Bi2223 filaments decreases in the region where Ag alloy sheath deforms plastically and Bi2223 filaments are expected to be elastic from macroscopic point of view. This deterioration may be reasonably understood when we take microscopic fracture that may precedes interior in the Bi2223 filaments, which may play important role in understanding performance of superconducting composites below irreversible strain. 4. Conclusions Strain of Bi2223 superconducting filaments in Ag-sheathed Bi2223 composite tapes under uniaxial tensile load has been evaluated by in situ synchrotron-radiation measurements in transmission. Residual strain in the as-supplied specimen was 0.05 ± 0.01% in compression. The relationship between strain in the filament and the average strain deviates from a linear one even in the region below reported irreversibility strain, where Bi2223 filaments are expected to be still elastic from macroscopic point of view. It suggests that the effective elastic modulus of the filaments decreases because of defect formation in a microscopic scale. Further examination on the microscopic defect formation and propagation, along with the role of soft Ag layer in Bi2223/Ag composite core should explain the reason of discrepancy between the macroscopic mechanical analysis and the present results. Acknowledgments
Fig. 7. Change of the average filament strain as a function of total strain. The slope of dot line is 1.0, corresponding to a fully elastic deformation. A polynomial fit up to the second power given by a broken line gives a good fit to the present experimental results.
The present experiment has been carried out as a Ôtrial-use programÕ under proposal No. 2003B0449 at SPring8. Part of the present experiment was supported by Grant-in-Aid for Scientific Research by the Ministry of Education, Science and, Technology under Grant 14350360.
H. Okuda et al. / Physica C 411 (2004) 114–119
References [1] J.W. Ekin, D.K. Finnemore, Q. Li, J. Trebrink, W. Carter, Appl. Phys. Lett. 61 (1992) 858. [2] O.O. Oduley, S.J. Pen, N. Alford, Supercond. Sci. Technol. 11 (1999) 858. [3] H. Kitaguchi, K. Itoh, H. Kumakura, T. Takeuchi, K. Togano, H. Wada, IEEE Trans. Appl. Supercond. 11 (2001) 3058. [4] J.K.F. Yau, N. Savvides, C.C. Sorrell, Physica C 266 (1996) 223. [5] S. Ochiai, K. Hayashi, K. Osamura, Cryogenics 33 (1993) 976.
119
[6] R. Passerini, M. Dhalle, E. Giannini, G. Witx, B. Seeber, R. Flueckiger, Physica C 371 (2002) 173. [7] L. Gherardi, P. Caracino, G. Cletta, Cryogenics ICEC Suppl. 34 (1994) 781. [8] R. Passeini, M. Dhalle, G. Witz, B. Seeber, R. Flueckiger, IEEE Trans. Appl. Supercond. 11 (2001) 3018. [9] S. Ochiai, T. Nagai, H. Okuda, S.S. Oh, M. Hojo, M. Tanaka, M. Sugano, K. Osamura, Supercond. Sci. Technol. 16 (2003) 988. [10] B. ten Haken, H.H.J. ten Kate, Physica C 20 (1996) 21. [11] For example, D. Balzard, J. Res. NIST 98 (1993) 321.
In situ strain measurements of Bi2223 superconducting filaments in multifilamentary Ag-sheathed Bi2223 superconducting tapes Hiroshi Okuda a,*, Kohei Morishita b, Shojiro Ochiai a, Dan Dokoh b, Motohide Matsui c, Hiroyuki Fujimoto c, Masugu Sato d b
a International Innovation Center, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan Graduate School of Materials Science and Engineering, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501, Japan c Railway Technical Research Institute, 2-8-3 Hikari, Kokubunji, Tokyo 185-8540, Japan d Japan Synchrotron Radiation Research Institute, 1-1 Kohto, Sayo-gun, Hyogo 679-5198, Japan
Received 21 April 2004; received in revised form 11 May 2004; accepted 31 May 2004 Available online 5 August 2004
Abstract In situ strain measurement was made for Bi2223 superconducting filaments in Ag-sheathed Bi2223 composite tapes utilizing synchrotron radiation. The residual strain was 0.05 ± 0.01% in compression. A small deviation from linear relationship between strain of the Bi2223 filaments and the average strain of the sample was found, meaning a decrease in elastic modulus of the filament even below the irreversible strain. 2004 Elsevier B.V. All rights reserved. PACS: 74.72.Hs; 85.25.Kx Keywords: Bi2223 superconducting composites; In situ strain measurement; Synchrotron radiation
1. Introduction Strain state of the Bi2223 filaments in silversheathed Bi2223 superconducting composite tape is very important to understand both the mechan-
*
Corresponding author. Tel.: +81 75 753 5193; fax: +81 75 753 4841. E-mail address: [email protected] (H. Okuda).
ical and the superconducting properties of the material [1–4]. Therefore, there has been several works to estimate the strain inside the composite based on the elastic–plastic mechanical analysis [5–9]. However, these analysis were based on mechanical modeling of the composite structure that required some assumptions concerning geometrical factors and mechanical properties of the constituent materials. Therefore, a direct measurement of strains of the constituent materials in the
0921-4534/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2004.05.019
H. Okuda et al. / Physica C 411 (2004) 114–119
composite under external load is quite important to predict the reliability of the superconducting composites in use. Ten Haken et al. [10] reported an in situ X-ray diffraction measurement of a model monocore Bi2212/Ag tape by Bragg geometry under an axial applied load, and showed that the Bragg peak shift is observed within the axial strain between 0.001 and +0.002. However, since we do not know a precise value of PoissonÕs ratio of the material, a direct measurement of the axial strain is needed for detailed analysis in order to make a full use of the merit of X-ray strain measurements [11]. In the present work, we conducted an in situ strain measurement of Bi2223 filaments in silver-sheathed multifilamentary Bi2223 tapes under tensile load in transmission (Laue) geometry utilizing synchrotron radiation.
2. Experimental The Ag-sheathed Bi2223 multifilamentary composite tape used in the present experiment was supplied by Korea Electrotechnology Research
115
Institute (KERI). The test samples were cut from the as-supplied 30 m role with 4 mm width and 0.31 mm thickness into short strips of 40 mm in length, and fixed in a set of grooved tabs by epoxy adhesive for tensile test pieces. As shown in Fig. 1, the composite tape consists of outer Ag–Mg alloy sheath and inner pure Ag/Bi2223 composite layer with 55 flat filaments of Bi2223. The volume fraction of the Ag alloy sheath, Bi2223 filaments and the pure Ag was 0.28, 0.42, and 0.30, respectively in the present sample. In order to measure strain free Bragg peaks from the filaments, Bi2223 filaments were extracted from the same composite tape by NH4OH/H2O2 solution. In situ strain measurements were carried out at Beamline 46XU of a synchrotron-radiation facility, SPring8, Japan. A small tensile test machine was mounted on a Huber 512.1 Eulerian cradle on a multiaxis diffractometer. The tensile load was applied by pulling up the upper beam by a geared pulsed motor. The load was monitored by a load cell attached directly to the upper beam. A top-view of the optical set-up in the present measurement is illustrated in Fig. 2(a).
Fig. 1. Cross-sectional view of Ag/Bi2223 composite tape used in the present experiment.
Fig. 2. (a) Schematic illustration of the present in situ measurement set-up. (b) Schematic illustration of the sample set in the in situ test machine. Note that the scattering vector is in parallel to the direction of tension.
116
H. Okuda et al. / Physica C 411 (2004) 114–119
A strong X-ray from an undulator was monochromatized into a beam of 22 keV with 0.1 · 0.5 mm2 in size, and introduced to the sample position. The shift of Bragg peak positions by the tensile load was measured in situ. The position of the sample was monitored by two charge-coupled device (CCD) telescopes. The center of the sample in thickness was controlled within 5 lm from the rotation center of the diffractometer for each scan using the CCDs. In the present slit conditions, this corresponds to the error in 2h within 1.5 · 104 degree at Bi2223 220 peak. As shown in Fig. 2(b), the Bragg peaks were measured in transmission geometry with h–2h configuration. Therefore, the direction of scattering vector is always parallel to the direction of tension. The strain measured in the present experiment directly corresponds to the strain in the direction of uniaxial tensile load.
3. Results and discussion The stress–strain curve of the composite tape obtained by a separate ex situ experiment is shown in Fig. 3. The strain was measured by a displacement of the markers attached at the both ends of the sample using CCD camera. The curve has three characteristic regions, and attributed to be [9], (I) the first elastic region where both Bi2223 filaments and Ag alloy sheath deform elastically, (II) the second region where Bi2223 filaments deform elastically and the Ag alloy sheath deforms plastically. In the last region (III), fracture of Bi2223 filaments characterizes a deformation with almost constant tensile stress. From Fig. 3, we chose four stress levels for the present strain analysis, namely, 0, 40, 90 and 140 N as shown by arrows in the figure. 0 and 40 N correspond to the region (I), 90 N the region (II), and 140 N at the end of region (II). In the following, we call the average strain corresponding to the strain in Fig. 3 as Ôtotal strainÕ, in order to distinguish from the strain of constituent components, i.e., the strain of Bi2223 filaments which is evaluated from the Bragg peaks. Fig. 4 shows the (2 0 0) Bi2223 Bragg peaks under applied tensile load. The intensity is normalized with respect to the incident X-ray flux monitor counts. The angle was corrected by the
Fig. 3. Stress–strain curve of the Ag/Bi2223 composite tape at room temperature. The stress levels used in the present experiment are shown by the arrows.
(1 1 1) diffraction peak of NIST standard Si powder painted with a solvent on the tape. The correction was within 2 · 103 degree for each scan. Since Bi2223 filaments have strong texture with their c axis normal to the tape face, clear peaks are observed only for 200 and 220 in the present measurement. The applied load was kept constant during measurement of a set of peaks for Bi2223, Si, and Ag. It is clearly seen that the peak position moves to the lower angle as the tensile load increases. The Bragg peak from extracted fibers, denoted by closed triangle in the figure, lies between the Bragg peaks for 0 and 90 N, almost close to the peak for 40 N. This result suggests that the residual strain of the Bi2223 filament in the as-supplied composite is in compression and should be equivalent to the external load of about 40 N. For more quantitative analysis, the peaks were fitted by using a Gaussian function. For the fitting, only the data larger than 70% of the peak intensity were used. By using the peak position of Bi2223 in the composites and the stress-free Bi2223 peak obtained for extracted fibers, the strain of Bi2223 filaments in the composite tape was calculated by 1 1 1 Da=a ¼ ; 2 sinðh0 Þ 2 sinðhcomp Þ 2 sinðh0 Þ ð1Þ
H. Okuda et al. / Physica C 411 (2004) 114–119
117
Fig. 4. The peak shift of Bi2223 200 under applied tensile load.
where h0 and hcomp are the peak positions of the extracted fibers and that for composites, respectively. The change of 220 Bragg peak under tensile load is shown in Fig. 5. Since the normalized peak intensity is almost the same order of magnitude as those of 200, the tape does not have a strong preferred orientation within the c plane. As seen in the figure, the shift of the peaks for 220 was quite similar to that for 200. Fig. 6 gives the strain in the Bi2223 fiber obtained from Eq. (1), as a function of applied load
Fig. 6. The filament strain obtained from 200 and 220 peak shift, as a function of applied load.
Fig. 5. The peak shift of Bi2223 220 under applied tensile load.
of the composite. The figure shows an almost linear relationship between the strain in the filaments and the applied load, and the strain state of the Bi2223 filaments turns from compressive to tensile when the applied load reaches 40 N, which corresponds to 35 MPa as average stress. The residual strain corresponds to the point where no external load is applied. Although the strains of the filaments obtained from 220 tend to be slightly smaller than that obtained from 200, the residual strains evaluated from the two indices agree well,
118
H. Okuda et al. / Physica C 411 (2004) 114–119
giving eR = 0.05 ± 0.01% as an average over two independent samples and the two indices. When we extrapolate the strain up to the fracture stress of the composite observed in the present experiment, 155 N, the maximum strain in the filaments at the fracture is estimated to be 0.17% in tension. Therefore, the Bi2223 filament has fracture strain close to 0.17%, and the composite has larger fracture strain of 0.22% for Bi2223 filaments because of the compressive residual strain of 0.05% in the Bi2223 filaments. For more detailed analysis, however, the strain of the Bi2223 filaments should be discussed in terms of the average strain of the composite, since the Bi2223 filaments support larger portion of load when the Ag alloy sheath deforms plastically. If the iso-strain condition holds during deformation of the composite, the total strain, the local strain of the Bi2223 filaments, and that of Ag sheath should agree as long as they deform uniformly, irrespective of whether it is elastic or plastic. To examine the point more clearly, the average filament strain is plotted as a function of total strain of the composite, eT, in Fig. 7. A least-square fit of the strain gives a small convex curvature, whose slope is 1.03 at eT = 0 and 0.58 at eT = 0.24%. As suggested above,
the slope should be unity for uniform deformation. Deviation from the linear relationship is observed in Fig. 7 even at a small total strain of 0.13%, which is well below the reported irreversible strain, this deviation suggests that we need to take the effect of microscopic defect in the Bi2223 filament in the region (II) into account. Therefore, we may safely conclude that effective elastic modulus of Bi2223 filaments decreases in the region where Ag alloy sheath deforms plastically and Bi2223 filaments are expected to be elastic from macroscopic point of view. This deterioration may be reasonably understood when we take microscopic fracture that may precedes interior in the Bi2223 filaments, which may play important role in understanding performance of superconducting composites below irreversible strain. 4. Conclusions Strain of Bi2223 superconducting filaments in Ag-sheathed Bi2223 composite tapes under uniaxial tensile load has been evaluated by in situ synchrotron-radiation measurements in transmission. Residual strain in the as-supplied specimen was 0.05 ± 0.01% in compression. The relationship between strain in the filament and the average strain deviates from a linear one even in the region below reported irreversibility strain, where Bi2223 filaments are expected to be still elastic from macroscopic point of view. It suggests that the effective elastic modulus of the filaments decreases because of defect formation in a microscopic scale. Further examination on the microscopic defect formation and propagation, along with the role of soft Ag layer in Bi2223/Ag composite core should explain the reason of discrepancy between the macroscopic mechanical analysis and the present results. Acknowledgments
Fig. 7. Change of the average filament strain as a function of total strain. The slope of dot line is 1.0, corresponding to a fully elastic deformation. A polynomial fit up to the second power given by a broken line gives a good fit to the present experimental results.
The present experiment has been carried out as a Ôtrial-use programÕ under proposal No. 2003B0449 at SPring8. Part of the present experiment was supported by Grant-in-Aid for Scientific Research by the Ministry of Education, Science and, Technology under Grant 14350360.
H. Okuda et al. / Physica C 411 (2004) 114–119
References [1] J.W. Ekin, D.K. Finnemore, Q. Li, J. Trebrink, W. Carter, Appl. Phys. Lett. 61 (1992) 858. [2] O.O. Oduley, S.J. Pen, N. Alford, Supercond. Sci. Technol. 11 (1999) 858. [3] H. Kitaguchi, K. Itoh, H. Kumakura, T. Takeuchi, K. Togano, H. Wada, IEEE Trans. Appl. Supercond. 11 (2001) 3058. [4] J.K.F. Yau, N. Savvides, C.C. Sorrell, Physica C 266 (1996) 223. [5] S. Ochiai, K. Hayashi, K. Osamura, Cryogenics 33 (1993) 976.
119
[6] R. Passerini, M. Dhalle, E. Giannini, G. Witx, B. Seeber, R. Flueckiger, Physica C 371 (2002) 173. [7] L. Gherardi, P. Caracino, G. Cletta, Cryogenics ICEC Suppl. 34 (1994) 781. [8] R. Passeini, M. Dhalle, G. Witz, B. Seeber, R. Flueckiger, IEEE Trans. Appl. Supercond. 11 (2001) 3018. [9] S. Ochiai, T. Nagai, H. Okuda, S.S. Oh, M. Hojo, M. Tanaka, M. Sugano, K. Osamura, Supercond. Sci. Technol. 16 (2003) 988. [10] B. ten Haken, H.H.J. ten Kate, Physica C 20 (1996) 21. [11] For example, D. Balzard, J. Res. NIST 98 (1993) 321.