抄録
Effects of pre-loading at room temperature on critical current at 4.2K of multifilamentary Nb3Sn superconducting composite wire heat-treated at 973K for 43 (sample A) and 259ks (B) were investigated. The main reults are summarized as follows. (1) It was predicted, based on Ekin's scaling law in combination with the elastic/plastic mechanical calculation, that the upper critical magnetic field and critical current can be improved by the pre-loading treatment through the control of the residual strain of Nb3Sn. This prediction was verified experimentally. (2) The strength distribution of Nb3Sn in sample A was estimated by applying the Weibull distribution function. The shape and scale parameters were 12 and 0.80GPa (standard length 1m), respectively. From these results, the average strengths for the length of 3 and 300m were calculated to be 0.70 and 0.48GPa, being lower than the strength of 1.0GPa for the short samples with a length of 25mm. (3) Using the strength distribution of Nb3Sn, Ekin's scaling law and the experimental data for the short samples, an attempt was made to deduce the influence of pre-loading on the critical current for long samples. It was shown for sample A with a length of 300m that the pre-stress level on the composites, at which the critical current is reduced due to the breakage of Nb3Sn, would be reduced by 20% in comparison with that for short samples of 25mm.
