Prediction of effective properties for composite superconducting strand and multi-stage cables

Abstract

Superconducting multifilamentary Nb3Sn strand and cables have complex microstructure and macrostructure which are used in the International Thermonuclear Experimental Reactor (ITER) superconducting magnet system. In a generic form, the superconducting strand is made of copper, multifilamentary Nb3Sn and bronze which is a composite. The twisted composite strands form the superconducting cables with typical multi-stage structures. Here we propose a numerical model focusing on the problem of characterizing the effective properties of composite superconducting strand and cables at microscopic and macroscopic scales. The effective elastic constants of the composite superconducting strand can be derived by involving the combination of the representative volume element (RVE) and the Mori-Tanaka method. Subsequently, the proposed method is applied to capture the effects of temperature on the effective elastic constants of the superconducting multi-stage cables. Results show the elastic constants predicted by this model agree well with existing theoretical predictions and available experimental data. This numerical model may be utilized to optimize the mechanical properties of the composite superconducting strand by tuning the constituent fractions and to control the tensile stiffness of superconducting cables by tuning the winding laps of the cables.