Multiscale analysis of the influence of the triplet helicoidal geometry on the strain state of a Nb3Sn based strand for ITER coils

A theoretical model of a beam of unidirectional composites - based on the homogenisation theory and a refined kinematical hypothesis - is used for the analysis of the influence of the helicoidal geometry of a superconducting strand triplet on its strain state. The triplet is the first cabling stage of the superconducting cables used to wind the coils of ITER fusion reactor. The multiscale modelling strategy is presented, for which a finite element code has been developed. A triplet of Nb3Sn based strands subjected to an axial stretch is analysed, and the resulting complete 3D strain state in the Nb3Sn filament is recovered. An “extra” strain is found due to the helicoidal geometry of the triplet. Discussion of the results concludes the paper.