Mechanical reinforcement mechanism of stainless-steel armor for flexible CORC cables under bending

Abstract CORC cables offer high current-carrying capacity and excellent bending flexibility, making them promising for applications in high-field magnets and high-capacity superconducting power equipment. However, the REBCO tapes in CORC cables are sensitive to strain and local contact loading, and their critical current may degrade when the cables are bent to small diameters. Although external stainless-steel armor has been experimentally demonstrated to improve the bending performance of CORC cables, the mechanisms underlying load sharing and local strain mitigation remain unclear. In this work, bending experiments and three-dimensional finite-element simulations are combined to investigate the mechanical reinforcement provided by an external stainless-steel armor layer in a CORC cable wound on a flexible interlocked stainless-steel former. By comparing armored and unarmored configurations at various bending diameters, we evaluate the interlayer contact pressure, strain concentration near the tape edges, and critical current variation under bending. The results show that, at the same bending diameter, the armored cable retains a higher normalized critical current than the unarmored cable. The bending-induced degradation is strongly layer-dependent and localized near the tape edges, primarily because of local contact-stress concentrations near the tape edges and interlayer overlap boundaries. Acting as an external constraint and load-sharing layer, the stainless-steel armor redistributes the bending load and reduces both the extent of the high-contact pressure regions and the average pressure over the effective contact area. Consequently, it weakens edge-dominated load transfer, suppresses local axial strain concentrations, and increases the minimum local critical current following bending and cooling. These results clarify the mechanical mechanisms by which external stainless-steel armor improves the bending performance of flexible CORC cables and provide guidance for armor design and the optimization of bending reliability in highly flexible REBCO cables.