An accurate estimation of the strain state of a strand inside a coil is a crucial point in the prediction of Nb3Sn conductor performance, since Nb3Sn strands show a strain-dependence of their critical parameters. This paper describes the results of a complex, nonlinear thermo-mechanical model suitably developed for superconducting wires. It is based on virtual testing of a properly chosen representative volume element. Provided that correct boundary conditions are considered, it is founded on a reliable and consistent micro-macro approach. To obtain the homogenized properties, seven boundary-condition elementary problems have to be solved at each chosen reference temperature. To exemplify the method, the equivalent properties of some ITER relevant strands are reported, for the mechanical and thermal field. Despite being an homogenization approach, it is possible to extract the strain values of the filament areas as well as of the other wire components in a easy way, and strain maps are shown. Furthermore, it is important to underline that initial material properties are unavoidably affected by uncertainties. In the same way, a certain variability is recorded on the measured data, depending upon many factors, e.g. handling of samples, different production billets, difficulties in measurements etc. Therefore, a great effort has been done to perform a sensitivity analysis of the influence of the material characteristics on the overall stress-strain behavior of the wire. This parametric study is reported in detail. Finally, to validate the method, homogenization results are compared with available experimental tests.
Superconducting Nb3Sn wires: a sensitivity analysis
BOSO, DANIELA;
2013
Abstract
An accurate estimation of the strain state of a strand inside a coil is a crucial point in the prediction of Nb3Sn conductor performance, since Nb3Sn strands show a strain-dependence of their critical parameters. This paper describes the results of a complex, nonlinear thermo-mechanical model suitably developed for superconducting wires. It is based on virtual testing of a properly chosen representative volume element. Provided that correct boundary conditions are considered, it is founded on a reliable and consistent micro-macro approach. To obtain the homogenized properties, seven boundary-condition elementary problems have to be solved at each chosen reference temperature. To exemplify the method, the equivalent properties of some ITER relevant strands are reported, for the mechanical and thermal field. Despite being an homogenization approach, it is possible to extract the strain values of the filament areas as well as of the other wire components in a easy way, and strain maps are shown. Furthermore, it is important to underline that initial material properties are unavoidably affected by uncertainties. In the same way, a certain variability is recorded on the measured data, depending upon many factors, e.g. handling of samples, different production billets, difficulties in measurements etc. Therefore, a great effort has been done to perform a sensitivity analysis of the influence of the material characteristics on the overall stress-strain behavior of the wire. This parametric study is reported in detail. Finally, to validate the method, homogenization results are compared with available experimental tests.
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