Applicability of Weibull Distribution to Description of Distributed Normalized Critical Current of Bent-Damaged Bi2223 Composite Tape

Ochiai, Shojiro; Okuda, Hiroshi; Sugano, M.; Hojo, Masaki; Osamura, Kōzō; Kuroda, T.; Kumakura, Hiroaki; Kitaguchi, Hitoshi; Itoh, K.; Wada, Hitoshi

doi:10.2320/matertrans.maw201001

Cited by 12 publications

(4 citation statements)

References 19 publications

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“…The unpredictable failure of the samples looks common due to the internal damage induced in the CC tape being a layered composite. Using the two-parameter Weibull distribution formula given by Hallinan [27], and Bernard's median rank [28], a Weibull plot of the mechanical delamination strength in a CC sample, especially in the case of Sample 1 using the 4 mm × 8 mm anvil, was derived and shown in figure 8. For this purpose, fourteen ( 14) tests were conducted.…”

Section: Mechanical Delamination Behaviourmentioning

confidence: 99%

Characterization of transverse tensile stress response of critical current and delamination behaviour in GdBCO coated conductor tapes by anvil test

Shin

Gorospe

2013

Supercond. Sci. Technol.

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Recent problems in superconducting devices operating at the high magnetic field regime include the possibility of substantial critical current, I c , degradation due to the delamination of the coated conductor (CC) tapes. The delamination may originate from excessive tensile radial stress and cleavage stress developed due to epoxy curing, cool-down and Lorentz force generated. Therefore, it is necessary to investigate the I c response under transverse loading and the delamination behaviour in REBCO CC tapes to predict its performance in practical device applications. In this study, using the anvil test method, the delamination strength and the transverse tensile stress response of I c in GdBCO CC tapes were investigated. Under transverse tensile stress, the I c degradation in GdBCO CC tapes showed both abrupt and gradual behaviours. A reversible I c degradation behaviour was also observed which was similar to the case under uniaxial tension. The electro-mechanical and mechanical delamination strengths were determined, wherein both increased when a smaller-sized anvil was used during the delamination test. The electro-mechanical delamination strength was approximately half of the mechanical delamination strength in the GdBCO CC tapes tested. Four delamination modes were observed and well correlated with electro-mechanical delamination strength and I c degradation behaviour. Lastly, delamination sites within the CC tapes were also correlated with the I c degradation behaviour that had been observed.

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Section: Mechanical Delamination Behaviourmentioning

confidence: 99%

Characterization of transverse tensile stress response of critical current and delamination behaviour in GdBCO coated conductor tapes by anvil test

Shin

Gorospe

2013

Supercond. Sci. Technol.

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“…In this case, the F(x), which denotes the cumulative fraction of the mechanical delamination strength values, was accurately estimated by Bernard's median rank shown in Eq. (3) [14].…”

Section: Mechanical Delamination Strengthmentioning

confidence: 99%

Delamination behaviors of GdBCO CC tapes under different transverse loading conditions

Gorospe¹,

Bautista²,

Shin³

2015

Progress in Superconductivity and Cryogenics

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In superconducting coil applications particularly in wet wound coils, coated conductor (CC) tapes are subjected to different type of stresses. These include hoop stress acting along the length of the CC tape and the Lorentz force acting perpendicular to the CC tape's surface. Since the latter is commonly associated with delamination problem of multi-layered CC tapes, more understanding and attention on the delamination phenomena induced in the case of coil applications are needed. Difference on the coefficient of thermal expansion (CTE) of each constituent layer of the CC tape, the bobbin, and the impregnating materials is the main causes of delamination in CC tapes when subjected to thermal cycling. The CC tape might also experience cyclic loading due to the energizing scheme (on -off) during operation. In the design of degradation-free superconducting coils, therefore, characterization of the delamination behaviors including mechanism and strength in REBCO CC tapes becomes critical. In this study, transverse tensile tests were conducted under different loading conditions using different size of upper anvils on the GdBCO CC tapes. The mechanical and electromechanical delamination strength behaviors of the CC tapes under transverse tensile loading were examined and a two-parameter Weibull distribution analysis was conducted in statistical aspects. As a result, the CC tape showed similar range of mechanical delamination strength regardless of cross-head speed adopted. On the other hand, cyclic loading might have affected the CC tape in both upper anvil sizes adopted.

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“…During the search for the cause of lower local I c values, two main mechanisms were identified in the investigations carried out by various groups: a weakening of vortex pinning in the superconducting layer, and a reduction of its cross-section [21][22][23][24][25][26]. If the properties of the superconducting material vary, the power-law exponent, n, is expected to fluctuate along the tape length [27][28][29]. On the other hand, when the locally lowered I c is caused by a simple reduction of the superconductor cross-section (e.g.…”

Section: Statistical Analysis and Evaluation Of The Overall Critical ...mentioning

confidence: 99%

Analysis of critical current fluctuations as a means of checking the quality of high-temperature superconductor tape slitting

Gömöry

Šouc

Godar

et al. 2023

Supercond. Sci. Technol.

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The patterns of longitudinal Ic fluctuations in the 12 mm wide production HTS tapes are compared with those obtained after slitting them to the widths of 6 mm, 4 mm and 3 mm, respectively. In the statistical analysis of Ic(x) data, the overall critical current, Ic,ovrl, was first calculated. In case of fluctuating critical current, Ic,ovr is lower than the average of critical current, Ic,aver. Also, the dissipation concentrates in the “weak spots” with reduced critical current. Simple model allows to estimate the thermal runaway current, Itr, at which the weakest location would convert to a “hot spot” with rapid increase of temperature. In the prediction of Itr, essential is the absolute minimum of Ic value, Icmin. Then, by comparing the Icmin/Ic,aver ratio in the slit tapes to that established previously for the manufactured tape, one can deduce if some new defects have been introduced during slitting. Interesting is also to check if the relation of Itr vs. Ic,ovrl remained without changing, because the lower of these two quantities represents the limit of transportable current. We have found a reduction of both Icmin/Ic,aver and Itr /Ic,ovrl ratios in some tapes, containing the edges of the original 12 mm production tape. Contrary to our expectations, the most serious drops in slit tapes were not in the same location as in the original tape. However, systematically better performance of the central strips (the tapes with both edges cut) is a strong indication that the most serious defects are created already during manufacturing, close to the tape edges. We conclude that the tape cutting by femtosecond laser has not introduced an additional non-uniformity. The analysis also shows that the criticality of defects in applications is largely governed by the width of said defect, the cooling conditions and the thickness of the stabilizing layer.

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Applicability of Weibull Distribution to Description of Distributed Normalized Critical Current of Bent-Damaged Bi2223 Composite Tape

Cited by 12 publications

References 19 publications

Characterization of transverse tensile stress response of critical current and delamination behaviour in GdBCO coated conductor tapes by anvil test

Characterization of transverse tensile stress response of critical current and delamination behaviour in GdBCO coated conductor tapes by anvil test

Delamination behaviors of GdBCO CC tapes under different transverse loading conditions

Analysis of critical current fluctuations as a means of checking the quality of high-temperature superconductor tape slitting

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