136 Bi2223 超伝導複合材料の変形挙動と超伝導特性の相関

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The strain dependence of the critical current, I_c, of Ag sheathed Bi2223 superconducting tapes has been studied under bending strain. Material used in this study was VAM1 of the VAMAS bending straining RRT program. The complex stress-strain behavior of each component was first analyzed in tension in order to understand the decrease of the critical current, I_c, due to the fracture of Bi2223 filaments. Here, the plastic deformation (work hardening) of Ag and Ag alloy, and thermal residual strain were taken into account. The difficulties are to determine several unknown parameters such as stress-strain behavior and the thermal expansion coefficients of each component. These are inversely decided to meet the global tensile stress-strain behavior and the thermal expansion of the composite tapes. The calculated stress-strain curves finally agreed well with experimental results. In bending analysis, the Bauschinger effect and the movement of neutral axis due to non-symmetric stress distribution were taken into account. The critical fracture strain of Bi2223 filament (=0.1%) was taken from the bending tests of extracted Bi2223 filaments by Passerini et al. The relative decrease of I_c with the increase of the Bi2223 tape curvature was calculated from the volume fraction of the broken filaments. The calculated value agreed well with the experimental results. Microscopic observation of the special distribution of filament fracture indicated that the fracture was observed at the outermost layer when the curvature was small, and then the location shifted inside layers. This behavior agreed well with the estimated location based on the above analysis.
社団法人日本機械学会の論文
2002-10-10

136 Bi2223 超伝導複合材料の変形挙動と超伝導特性の相関

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