Correlation between mesoscopic mechanical behavior and superconductivity for multifilamentary superconducting composite wire

本文研究了Nb-Ti/Cu和Nb_3Sn/Cu多芯超导复合线材的超导细丝和基体铜的形变和断裂。研究从细观角度出发，考虑了复杂的热残余应力。研究了形变与超导电性的关系。（1）Nb_3Sn/Cu/Cu-Sn/Nb复合丝材中Cu和Cu-Sn的力学性能：从Nb_3Sn/Cu/Cu-Sn/Nb复合丝材中去除Cu成分，通过比较有无Cu成分的应力-应变曲线，得到了Cu和青铜成分的应力-应变曲线。除了这些详细的实验程序，在本研究中考虑的热残余应力在铜相的不均匀性。为了确定应变在铜相中的分布，对复合材料进行了试验， ...更多信息 去除了一定量的铜。(2)Nb_3Sn/Cu复合丝中Nb_3Sn丝的力学性能：用硝酸从复合丝中提取Nb_3Sn丝，然后用环氧树脂浸渍。用混合律计算了Nb_3Sn丝的杨氏模量。结果表明，Nb_3Sn纤维的杨氏模量比文献报道的值要小。(3)Nb-Ti/Cu复合线材的微观疲劳断裂过程为：疲劳裂纹在稳定铜周围萌生，并贯穿线材横截面，切断Nb-Ti细丝。疲劳加载后的残余强度和临界电流都与剩余丝数有很好的相关性。(4)Nb-Ti/Cu复合丝中单丝的多重颈缩：通过改变退火温度至500℃，研究了Nb-Ti丝和铜的力学性能对多重颈缩形成的影响。随着退火温度的升高，铜的屈服应力降低，并观察到广泛的加工硬化。在500℃退火时，发生了多次颈缩。实验观察到。这种行为也证实了使用有限元法的数值变形分析。少

Deformation and fracture of superconducting filaments and matrix copper were investigated for multifilamentary Nb-Ti/Cu and Nb3Sn/Cu superconducting composite wires. The researches were conducted from the mesoscopic view point, and the complicated thermal residual stresses were taken into account. Then the correlation between the deformation and superconductivity were studied. The results are summarized as follows:(1) Mechanical properties of Cu and Cu-Sn in Nb_3Sn/Cu composite wires:The copper component was removed from the Nb_3Sn/Cu/Cu-Sn/Nb composite wire, and comparison of the stress-strain curves with and without copper component yielded the stress-strain curves of the copper and bronze component. In addition to these detailed experimental procedures, the non-uniformity of the thermal residual stress in copper phase was taken into account in the present study. In order to confirm the strain distribution in copper phase, the test was carried out with the composites from which half … More amount of copper was removed.(2) Mechanical properties of Nb3Sn filaments in Nb_3Sn/Cu composite wires:The Nb_3Sn filaments were extracted from the composite wire with nitric acid, and then impregnated with epoxy resin. The Young's modulus of Nb_3Sn filament was calculated using the rule of mixture. The results indicated that the Young's modulus of Nb_3Sn filament was smaller than already reported values.(3) Microscopic fatigue fracture process in Nb-Ti/Cu composite wires:Fatigue cracks initiated at the surrounding stabilizer copper, and went through the transverse section of the wire, cutting Nb-Ti filaments. Both the residual, strength of fatigued wire and the critical current after fatigue loading were well correlated to the number of remaining filaments.(4) Multiple necking of filaments in Nb-Ti/Cu composite wires:The effect of mechanical properties of Nb-Ti wire and copper on the formation of multiple necking was investigated by changing the annealing temperature up to 500℃. For higher annealing temperature, the yield stress of copper decreased and extensive work hardening was observed. At the annealing temprature of 500℃, the multiple necking. was experimentally observed. This behavior was also confirmed by the numerical deformation analysis using finite element method. Less