A novel numerical mechanical model for the stress–strain distribution in superconducting cable-in-conduit conductors

Abstract

Besides the temperature and magnetic field, the strain and stress state of the superconducting Nb3Sn wires in multi-stage twisted cable-in-conduit conductors (CICCs), as applied in ITER or high field magnets, strongly influence their transport properties. For an accurate quantitative prediction of the performance and a proper understanding of the underlying phenomena, a detailed analysis of the strain distribution along all individual wires is required. For this, the thermal contraction of the different components and the huge electromagnetic forces imposing bending and contact deformation must be taken into account, following the complex strand pattern and mutual interaction by contacts from surrounding strands. In this paper, we describe a numerical model for a superconducting cable, which can simulate the strain and stress states of all single wires including interstrand contact force and associated deformation. The strands in the cable can be all similar (Nb3Sn/Cu) or with the inclusion of different strand materials for protection (Cu, Glidcop). The simulation results are essential for the analysis and conductor design optimization from cabling to final magnet operation conditions. Comparisons are presented concerning the influence of the sequential cable twist pitches and the inclusion of copper strands on the mechanical properties and thus on the eventual strain distribution in the Nb3Sn filaments when subjected to electromagnetic forces, axial force and twist moment. Recommendations are given for conductor design improvements.

Optimization of ITER Nb3Sn CICCs for coupling loss, transverse electromagnetic load and axial thermal contraction

“…It appears up to now that for simulation of the evolution of the coupling loss with cycling in the press, a deviation can occur of about a factor of two at high bumber of cycles. It is demonstrated that the amount of critical current degradation from transverse load [60], [61] is subject to interference due to different sub-cable twist pitches, we expect a similar behavior for coupling loss. This opens scope for optimisation of the twist pitch sequence for CICCs to minimise the transverse load degradation, the warm-up cool-down degradation and the coupling loss.…”

Stress–Strain Distribution Analysis in Bi2212 Subcable Based on Numerical Modeling and Experiment

“…Several models [8]- [10] have been introduced to analyze the cable pattern for Nb3Sn or NbTi CICC, including cabling and conductor operation at low temperature. Large tension on strands and cable can cause undesired single strand elongation or damage during cabling.…”

“…In this paper, the results are reported of investigations on a cable made of three single Bi2212 round wires with different pitches subjected to tensile stress-strain tests at 300 K. The mechanical properties were analyzed by a numerical cable model [10]. The experimental results were compared to the numerical model for conditions at 300 K. Then the model was used to analyze the strain distribution of a single wire in different cable configurations at room and cryogenic temperature.…”

Modeling for mechanical response of CICC by hierarchical approach and ABAQUS simulation

“…Thus, the investigation on local stress and strain distribution map is insufficient [16]. Besides, Qin et al [17,18] develop a theoretical mechanical model (CORD) for a superconducting cable based on wire rope theory. CORD can predict the local strain and stress state of all individual wires, including inter-strand contact force and the associated deformation.…”