Characterization of super conducting property from the interdisciplinary viewpoint of superconducting materials technology and solid mechanics

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The superconducting properties such as critical temperature, current and upper magnetic field change when mecahnical and electro-magnetic forces are exterd on the superconducting wires during fabrication and/or service. In this work, by combining the knowledges in the fileds of superconducting materials and mechanics, the nucleation, growth and accumulation of damages under staic and cyclic stresses and their influences on superconduing properties of Nb_3Al and Nb-Ti composite wire were clarified. Main results are summaized as follows. (1) The preferred orientation of the filaments and stabilizing copper were clarified by the neutron diffraction method. (2) Nb_3Al filament is broken in a brittle manner, while Nb-Ti one, having ductility, shows mumtiple necking due to the mechanical in teraction with surrounding copper, which acts to keep high critical current density up to high applide strain. (3) In spite of large scatter of strength of Nb_3Al filaments, the scatter of strength of composite wire is small. This feature could be reproduced by a Monte Carlo simulation method in the compuetr. The present results first demonstrate the high reliability of composite wire. (4) Under cyclic stress, crack forms first in the copper (stage I)) and propagate into the core portion(Stage II). In this process, filamenst are broken, resulting in low critical current and low residual strength.