NB3SN TENSILE-STRENGTH AND ITS DISTRIBUTION ESTIMATED FROM CHANGE IN SUPERCONDUCTING CRITICAL-CURRENT OF PRELOADED MULTIFILAMENTARY COMPOSITE WIRE

The distribution of tensile strength of Nb3Sn in multifilamentary comp osite wires heat-treated at 973 K for 8.64 ks (sample A) and for 43.2 ks (sample B) was estimated from an analysis of the change in the supe rconducting critical current at 4.2 K caused by the preloading treatme nt at room temperature. The average strengths of Nb3Sn in samples A an d B for a gauge length of 25 mm were 1.3 and 1.0 GPa, respectively. Ap plying the two-parameter Weibull distribution function, the shape para meters of samples A and B were 7.2 and 12 and the scale parameters 1.4 and 1.1 GPa, respectively. These results indicate that when the thick ness of Nb3Sn becomes great, the average strength becomes low, while t he scatter of the strength (the coefficient of variation) becomes smal l.