ブロンズ法Nb₃Sn線材の臨界温度の軸方向および横方向応力/歪依存性

抄録

The critical temperatures, T_c, have been resistively measured as functions of axial tensile strain and transverse compressive stress for bronze processed Nb₃Sn single-core wires or tapes with various volume ratios of bronze matrix to Nb core. For the case of axial tensile strain, T_c's first increase with externally applied strain, reach their maxima and then decrease with further increasing strain, as reported for the critical current, I_c, under applied strain. Increases in T_c due to applied strain and strains where T_c's reach their maxima become larger with increasing the volume ratio of the bronze matrix to the Nb core. These results confirm that T_c measurements under applied strain are very effective to predict I_c under applied strain. The strain dependence of T_c is quantitatively analyzed based on phenomenological theory by Welch, and it is shown that the difference in the T_c-degradation before and after the maximum in T_c may be interpreted in terms of the relative significance of hydrostatic and nonhydrostatic components of strain in altering T_c. For the case of transverse compressive stress, T_c's decrease monotonically with externally applied stress. It is shown that there is no large difference in the T_c-degradation with stress between transverse compressive stress and axial tensile stress in contrast with the results on I_c reported.