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Influences of cracking of coating layer under applied tensile strain on V(voltage)-I(current) curve, critical current, and n-value of DyBa2Cu3O7-δ coated conductor were studied experimentally and analytically. The experimentally measured variations in V-I curve, critical current, and n-value with increasing applied strain and the correlation of n-value to critical current were described well by the partial crack-current shunting model of Fang et al. Also, the variations in the ratio of shunting current to overall critical current and the ratio of voltage developed in the cracked region to overall voltage with extension of crack, and the variation in critical current with the ratio of noncracked area to overall cross-sectional area of superconducting layer were revealed. [ABSTRACT FROM AUTHOR]

An approach to predict the variation in critical current with applied tensile/bending strain of Bi2223/Ag/Ag alloy composite tapes from the tensile stress-strain curves was presented. Three different fabrication-route samples were used to examine the applicability of the present approach. The damage strain parameter, referring to the difference between the tensile fracture strain and residual strain of Bi2223 filaments along the sample length direction (current transport direction), was estimated from the variation in the slope of the tensile stress-strain curve. With the estimated damage strain parameter, the irreversible tensile strain for critical current was predicted, which agreed well with the experimental result in all samples. Also by substituting the estimated damage strain parameter into the core shape—incorporated model, the critical current-bending strain curve was predicted, which described satisfactorily the experimental result in all samples. The present approach could be a useful tool for prediction of critical current-dependence on applied tensile/bending strain. [ABSTRACT FROM AUTHOR]

Abstract: It was attempted to estimate the distribution of irreversible bending strain for critical current of the Bi2223 composite tape. In the modeling, the shape of the core composed of the current transporting Bi2223 filaments and Ag, and the damage strain parameter given by the difference between the intrinsic tensile damage strain and residual strain of the Bi2223 filaments, were incorporated to describe the damage evolution in the core and its relation to critical current. The application of the model to the experimental results of critical current-bending strain relation for many test specimens revealed that the distribution of the irreversible bending strain is described by the two parameter Weibull distribution function. Based on discussion about the influence of the core geometry on the irreversible strain and the result of analysis of the experimental data, a simple and practically useful method was proposed for estimation of the distribution of irreversible bending strain. [Copyright &y& Elsevier]

Abstract: It was attempted to estimate the Young’s modulus, thermally induced residual strain, intrinsic fracture strain and the coefficient of thermal expansion at room temperature of the Bi2212 filaments in Bi2212/Ag/Ag alloy composite wire by combining the results of tensile test, X-ray diffraction measurement and thermomechanical analysis. The Young’s modulus of the Bi2212 filaments was estimated to be 66.3GPa from the analysis of the stress–strain curve of the composite. The thermally induced residual strain of Bi2212 filaments introduced during cooling due to the difference in thermal expansion among the constituents (Bi2212, Ag and Ag alloy) was estimated to be −0.14% by in situ synchrotron-radiation diffraction. The intrinsic fracture strain of Bi2212 filaments was 0.11–0.13% from the analysis of the stress–strain curve of the composite wire, in which the estimated residual strain was substituted. The coefficient of thermal expansion of the Bi2212 filaments was estimated to be 11.5×10−6 K−1 from the analysis of the thermal expansion of Bi2212 composite wire measured between 300K and 400K in combination with the property values estimated from the tensile test results. [Copyright &y& Elsevier]

Abstract: The scatter of critical current of bent Bi2223 composite tape was analyzed from a statistical viewpoint. It was revealed that the increase in scatter of the critical current beyond the irreversible bending strain is attributed to the heterogeneous damage evolution. Further modeling analysis, based on the heterogeneous damage evolution, revealed that the distribution of the damage strain parameter-value, which refers to the difference between the intrinsic tensile damage strain and residual strain of the Bi2223 filaments, is described by the two parameter Weibull distribution function, from which the distribution of the normalized critical current value is described by the three parameter Weibull distribution function. [Copyright &y& Elsevier]

Abstract: Local and overall transport critical current I C and n-value at 77K of multifilamentary Bi2223-composite tape were studied under applied tensile and bending strains. The I C and n-value of the local elements constituting of the overall sample and those of the overall sample were measured for the voltage probe distances 10 and 60mm, respectively. The local I C as well as n-value varied along the sample length under both tensile and bending strains, while the critical current reduction process under the tensile strain was quite different from that under bending one; a big difference in damage among the local elements was found under tensile strain but not under bending one. While the damage process was different between the tensile and bending strains, the relation of overall I C and n-value to the local ones was described comprehensively by the voltage summation model. From the analysis of the experimentally observed critical current–applied strain relation of the local elements, the variation of the critical current determining factor “fracture strain–residual strain” along the sample length was revealed. [Copyright &y& Elsevier]

Abstract: It has been reported that, when the (Bi,Pb)2Sr2Ca2Cu3Ox (hereafter noted as BSCCO)/Ag/Ag-alloy tape is laminated with stainless steel, the tensile strain tolerance of critical current is much improved. In this study, using the non-laminated and laminated BSCCO composite tapes fabricated at American Superconductor Corporation, the influences of lamination on the critical current and its distribution under bending strain were studied. The analysis of the measured variation of average critical current with bending strain based on the damage evolution model revealed that the laminated stainless steel acts to suppress the fracture of the BSCCO filaments. The experimentally observed high critical current retention of the laminated tape up to high bending strain was accounted for by the suppression of fracture of BSCCO filaments stated above and enhancement of the compressive residual strain in the filaments. The distributions of local critical current in non-laminated and laminated composite tape were described well by the three-parameter Weibull distribution function within the bending strain lower than 1.1%. The coefficient of variation of distribution of critical current of the laminated tape was similar to that of the non-laminated one under the same strain distribution in the core. [Copyright &y& Elsevier]

Abstract: Using the high critical current type BSCCO composite tape fabricated at American Superconductor Corporation, the relation of overall critical current to the distribution of local critical current and the dependence of overall critical current on sample length of the bent samples were studied experimentally and analytically. The measured overall critical current was described well from the distribution of local critical current and n-value of the constituting short elements, by regarding the overall sample to be composed of local series circuits and applying the voltage summation model. Also the dependence of overall critical current on sample length could be reproduced in computer satisfactorily by the proposed simulation method. [Copyright &y& Elsevier]

Abstract: As the stress-induced damage evolution is different from position to position in a sample, the local critical current is scattered, affecting on the overall current. In the present work, the correlation between the local and overall currents at 77K in a multifilamentary Bi2223/Ag/Ag alloy composite tape bent by 0.4% and 0.7% at room temperature was studied. It was found that the critical current and n-value of the overall sample composed of the local elements with different critical current and n-value were described comprehensively with a voltage summation model for both bending strains 0.4% and 0.7%. Also the regression analysis revealed that the distribution of local critical current could be described by the three parameter-Weibull distribution function at both bending strains. The experimental results for overall sample could be described well by a Monte Carlo simulation for both bending strains. [Copyright &y& Elsevier]

Abstract: The strain dependence of the critical current, I c, of Bi2223/Ag/Ag-alloy composite superconducting tapes has been studied both experimentally and analytically under bending deformation. The microscopic observation after bending deformation indicated that delamination existed inside Bi2223 filaments and filament/matrix interface. Then, the former bending deformation analysis was modified to fit the existence of the delamination. The calculated critical current, I c, was almost the same as the experimental results when the delamination is fully located at the mid plane of the tape though the actual situation was partial in the width direction. Then the location of the delamination was moved in the thickness direction in the analysis. The calculated I c agreed well with the experimental results when the delamination location was moved to the compressive side. [Copyright &y& Elsevier]

Abstract: An inter-comparison program (round-robin-test) aimed at the establishment of a standard test method for the bending strain effect on the critical current in Ag alloy-sheathed Bi-2223 tapes was implemented with participation of 12 laboratories around the world. Samples were bent at room temperature using bending devices that were specially designed for this RRT. The critical current was measured at 77K and in the self-field. After critical current measurement of an unbent sample, bending of the sample and subsequent critical current measurements were done from 0.2% to 1.0% in 0.2% steps of strains on a single sample. Reported data from participants showed that the critical current values start to decrease from 0.4% strain and continue to decrease to 1.0% strain. Moreover, the data scatter starts to increase stepwise at 0.4% strain, being correspondent to the variation in the critical current values with bending strain, and it continues to increase gradually to 1.0% strain. The coefficient of variation values are 2.5%, 5.1% and 6.4% for 0%, 0.4% and 1.0% bending strain, respectively. Results were also compared in terms of the irreversible bending strain. Possible sources of error are discussed. [Copyright &y& Elsevier]