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

点击翻译按钮获取中文摘要

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