Analysis of critical current distribution of bent Bi2223 composite tapes by unifying parameterapproach and its application to the description of average critical current–bending strainrelation near the average irreversible strain

Abstract

When the critical current of bent Bi2223 composite tape is measured for manyspecimens, the critical current value is different from specimen to specimen, beingdistributed from low to high values. We need to characterize the distribution ofcritical current at various applied strains and also to predict the distribution ofirreversible strain for reliability and safe design. The present work attempted todescribe them from the statistical viewpoint. In the analysis, the unifying parameterapproach proposed recently by the authors was employed, in which the differencein damage evolution and critical current among the specimens was correlatedwith the distribution of the unifying parameter that refers to the tensile damagestrain of Bi2223 filaments in composite tapes. By application of this approachto the measured critical current values under various bending strains for threeBi2223 composite tapes from different suppliers (VAM1, VAM2 and VAM3 usedas the common test samples in the round robin test of VAMAS/TWA16), theunifying parameters were estimated and were formulated by the Weibull distributionfunction. With the formulated distribution function of the unifying parameter,the distributions of the critical current at various strains, the distribution of theirreversible bending strain and the average critical current—bending strain relationnear the average irreversible bending strain could be described satisfactorily.