Bending of silver-sheathed (Bi,Pb)-2223 tapes investigated by magneto-optical flux visualization

Koblischka, Michael Rudolf; Johansen, T. H.; Bratsberg, H.

doi:10.1088/0953-2048/10/9/010

Cited by 28 publications

(13 citation statements)

References 42 publications

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“…As an explanation, it was argued that the flux patterns are mainly due to the intergranular currents, with a negligible contribution of the intragranular currents. 15,21 Our results on the model sample now confirm this explanation. Even at low temperatures, where effects of granularity are important, a dark d ϩ line can be observed in the center of the tapes as shown in Refs.…”

Section: B Flux Distributionssupporting

confidence: 78%

Flux penetration into an artificially granular high-Tcsuperconductor

et al. 1999

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A YBa 2 Cu 3 O 7Ϫ␦ thin film is patterned into a hexagonal close-packed lattice of disks (2rϭ50 m) which are touching each other at the circumferences in order to enable the flow of an intergranular current. Such a sample was suggested by Koblischka et al. ͓Appl. Phys. Lett. 70, 514 ͑1997͔͒ as a model for a layered granular structure like in a (Pb,Bi) 2 Sr 2 Ca 2 Cu 3 O 10ϩ␦ ͑Bi-2223͒ tape. The magnetization measurements reveal an anomalous position of the low-field peak ͑central peak͒ similar to Bi-2223 tapes. Magneto-optic imaging is employed to visualize the local-field distributions. At low magnification, the flux patterns in the intergranular area between the disks are observed. The observations at high magnification reveal the flux penetration and pinning within the disks. It is shown that such samples may serve as model samples for granular high-T c superconductors.

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Section: B Flux Distributionssupporting

confidence: 78%

Flux penetration into an artificially granular high-Tcsuperconductor

et al. 1999

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“…Similar studies have been performed [7], [8] where the samples are bent at room temperature, and then inserted into the MOI cryostat. In this work, longitudinal strain is applied to Bi-based tapes within the MOI cryostat while at the same time the crack formation is observed.…”

Section: Introductionmentioning

confidence: 84%

Strain effects in high temperature superconductors investigated with magneto-optical imaging

Laan

Eck

Haken³

et al. 2003

IEEE Trans. Appl. Supercond.

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Abstract-In order to determine the influence of intermediate deformation steps on the mechanical behavior of Bi-based tapes, the effect of longitudinal applied strain is investigated by means of magneto-optical imaging. The strain is applied in a helium flow-cryostat. Cracks appear soon after the critical current in Bi-based tapes is degraded. All filaments form multiple cracks that grow into tape-wide cracks, running from one filament to the next. The crack location is not caused by stress concentrations in the matrix, but by the mechanically weak colony boundaries. Because of the absence of intermediate rolling steps in the production of Bi 2 Sr 2 CaCu 2 O tapes, a different crack structure is observed compared to Bi 2 Sr 2 Ca 2 Cu 3 O tapes. The relation between the critical current and the formation of cracks is studied. The degradation in critical current before the critical strain is reached may be caused by microcracks that remain undetected by magneto-optical imaging. The influence of strain on the microstructure of YBa 2 Cu 3 O coated conductors is also investigated with magneto-optical imaging. The formation of cracks is believed to be determined by the nickel substrate and related to the Ni-grain size.

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“…Earlier studies [13,14] investigated the influence of bending strain on the current paths in the filaments. The samples were bent at room temperature and subsequently cooled down to make the MO-image.…”

Section: In Situ Observation Of Crack Formationmentioning

confidence: 99%

Critical current versus strain research at the University of Twente

Eck

Laan

Dhallé

et al. 2003

Supercond. Sci. Technol.

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At the University of Twente a U-shaped spring has been used to investigate the mechanical properties of a large variety of superconducting tapes and wires. Several mechanisms are responsible for the degradation of critical current as a function of applied strain. A change in its intrinsic parameters causes a reversible critical current dependence in Nb 3 Sn. The critical current reaches a maximum at a wire-dependent tensile strain level, and decreases when this tensile strain is either released or further increased. In Bi-based tapes the critical current is virtually insensitive to tensile strain up to a sample-dependent irreversible strain limit. When this limit is exceeded, the critical current decreases steeply and irreversibly. This behaviour is attributed to microstructural damage to the filaments. This cracking of the filaments is verified by a magneto-optical strain experiment. Recent experiments suggest that in MgB 2 the degradation of critical current is caused by a change in intrinsic properties and damage to the microstructure. Magneto-optical imaging can be used to investigate the influence of applied strain on the microstructure of MgB 2 , as is done successfully with Bi-based tapes. In all these conductors the thermal precompression of the filaments plays an important role. In Nb 3 Sn it determines the position of the maximum and in Bi-based and MgB 2 conductors it is closely related to the irreversible strain limit.

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Bending of silver-sheathed (Bi,Pb)-2223 tapes investigated by magneto-optical flux visualization

Cited by 28 publications

References 42 publications

Flux penetration into an artificially granular high-Tcsuperconductor

Flux penetration into an artificially granular high-Tcsuperconductor

Strain effects in high temperature superconductors investigated with magneto-optical imaging

Critical current versus strain research at the University of Twente

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