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

Abstract

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