Bronze-processed multifilamentary Nb3Sn superconducting composite wires were loaded and then unloaded at room temperature, resulting in a large change in the critical current (Ic) and the upper critical magnetic field (Hc2) at 4.2 K: the Ic and Hc2 increased, reaching maximum and then decreasing with an increasing applied stress level. The changes in Ic and Hc2 below the loading stress to cause breakage of the Nb3Sn were described well from the viewpoint of the change in residual strain in Nb3Sn. When the applied stress was high enough to cause breakage of the Nb3Sn, the I c was reduced seriously. From the reduction in Ic in such a case, the strength distribution of Nb3Sn was estimated by using the Weibull distribution function. The result indicated that the shape parameter for the Weibull distribution was 12 and the average strength was 1.02 GPa in the present samples. From the calculation of the residual strain at 4.2 K in combination with the estimated strength distribution of Nb3Sn, the change in Ic at 4.2 K as a function of applied stress at room temperature could be described well.
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