Mechanical-electrical modeling of stretching experiment on 45 Nb3Sn strands CICCs

Cable-In-Conduit Conductors made with Nb3Sn strands will be used in ITER magnets. The current carrying capability of these Nb3Sn strands is known to be highly dependant on the strain state resulting from mechanical loading. The intricate cabling pattern of CICC, added to the thermal differential shrinkage between conductor jacket and Nb3Sn filaments induce complex strand trajectories and a highly inhomogeneous strain state. This 'cable strain map' also evolves with operating loads (Lorentz force/hoop stress). The SAMAN experiment, conducted in the FBI facility at Karlsruhe Institute of Technology, aimed to stretch sub-size, ITER-like conductors, in order to observe the evolution of the critical current associated with these loadings. The application of the Multifil finite element code, developed at Ecole Centrale de Paris, has helped quantifying the local strains along every individual strand, and their evolutions during cooldown (from heat treatment), energizing and stretching phenomena. Using Multifil output mechanical data as input in the CEA electrical code CARMEN has allowed computing the critical current in every strand, thus leading to an understanding of the critical current degradation of such sub-size conductors. This paper shows, for two SAMAN samples, what is the impact of bending strain concentration on a CICC current transport capability. (authors)