Nonlinear contact behavior of HTS tapes during pancake coiling and CORC cabling

Abstract

Both the pancake coiling and conductor on round core (CORC) cabling processes consist of winding second-generation high-temperature superconducting tape (REBCO) in a core. The contact behavior between the tape and the core during the winding process directly affects the critical current, cable flexibility, mechanical support and electrical contact resistance. Therefore, the winding process needs to be optimized to produce pancake coils and CORC cables with the desired electrical and mechanical properties. This paper comprehensively considers the role of the relaxation and Poisson effects. The theoretical model and the finite element model (FEM) for calculating the contact stress during the winding process are established, and a formula for the estimation of the contact force is proposed. The suitable winding pre-tension force, winding curvature radius of SCS2030 (2 mm width and 30 μ m substrate thickness) and SCS4050 (4 mm width and 50 μ m substrate thickness) of REBCO tapes are obtained and discussed by accounting for the relaxation effect and the critical current degradation limit. With consideration of the Poisson effect, the nonlinear contact behavior is investigated. In addition, the relaxation effect, Poisson effect and plasticity of the REBCO tape are taken into account in the FEM model. The results show that the axial strain in the REBCO layer during the winding process is related to the contact behavior. The greater the winding pre-tension force, the smaller the helical curvature radius, and the greater the contact force. The distribution of contact stress for several winding factors (winding pre-tension force, winding angle and the core radius) is divided into three contact types: the single-line contact, the double-line contact and the surface contact. The FEM model results are consistent with the theoretical evaluation and are more suitable for practical winding cases. This research is the basis for designing and optimizing pancake coils and CORC cables.

Investigating the effect of transverse compressive loads on the electromagnetic performance of superconducting CORC® cables

“…The work on CORC cables [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] is either treating the mechanical, electromagnetic, or critical transport characteristics, lacking a model so far that simultaneously handles mechanical and electromagnetic properties. Consequently, a 3D numerical model of the CORC cable is established based on the T-A formulation and the FE method.…”

“…where Q is in units of J/cycle, and 1/f is the period of the applied background sinusoidal magnetic field. A Dirichlet-Neumann boundary condition is imposed on the outer boundary of the 3D air domain to simulate the applied background magnetic field (see figure 4): B = ((B 0 sin(2πft) 0 0) (10) where B 0 is the magnitude of the AC magnetic field, f is the frequency.…”

“…The mechanical and electromagnetic response of CORC cables has attracted significant attention because of their importance for magnet design and optimization [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Anvar et al [8] presented finite element (FE) modeling of the stressstrain state of CORC cables and wires under bending loads.…”

“…Subsequently, analytical and FE models were also developed to predict the performance of CORC wires under axial tensile strain [9]. Wang et al [10] investigated the nonlinear contact behavior of the CORC cable from theoretical and FE perspectives, and a formula for estimating the contact force was proposed. They evaluated the performance of CORC cables under axial tensile loading.…”

Prediction of strain, inter-layer interaction and critical current in CORC® wires under axial strain by T-A modeling

“…To determine the effect of the REBCO tape strain on the CORC ® wire performance, Anvar et al studied the bending flexibility of CORC ® wires by combining experiments with a finite element model and considering the effect of the winding process on the REBCO layer strain [21]. Wang et al calculated the nonlinear contact characteristics and deformation of the HTS tape under different winding parameters during CORC ® cabling by simulation and theoretical method [22]. van der Laan et al conducted uniaxial tensile tests of multilayer CORC ® wires in liquid nitrogen, studying the performance degradation of CORC ® wires under monotonic and cyclic axial loads [23].…”