For high current superconductors in high magnet fields with currents in the order of 50 kA, single ReBCO coated conductors must be assembled in a cable. The geometry of such a cable is mostly such that combined torsion, axial and transverse loading states are anticipated in the tapes and tape joints. The resulting strain distribution, caused by different thermal contraction and electromagnetic forces, will affect the critical current of the tapes. Tape performance when subjected to torsion, tensile and transverse loading is the key to understanding limitations for the composite cable performance. The individual tape material components can be deformed, not only elastically but also plastically under these loads. A set of experimental setups, as well as a convenient and accurate method of stress-strain state modeling based on the finite element method have been developed. Systematic measurements on single ReBCO tapes are carried out combining axial tension and torsion as well as transverse loading. Then the behavior of a single tape subjected to the various applied loads is simulated in the model. This paper presents the results of experimental tests and detailed FE modeling of the 3D stress-strain state in a single ReBCO tape under different loads, taking into account the temperature dependence and the elastic-plastic properties of the tape materials, starting from the initial tape processing conditions during its manufacture up to magnet operating conditions. Furthermore a comparison of the simulations with experiments is presented with special attention for the critical force, the threshold where the tape performance becomes irreversibly degraded. We verified the influence of tape surface profile non-uniformity and copper stabilizer thickness on the critical force. The FE models appear to describe the tape experiments adequately and can thus be used as a solid basis for optimization of various cabling concepts.

A CORC ® cable is composed of several layers of helically wound high-temperature superconducting (HTS) tapes on a round core with the winding direction reversed in each successive layer. The cable is flexible but the flexibility is limited by the critical strain value causing breakage of the HTS layer when this strain level is exceeded. The cables for magnets in fusion reactors experience large mechanical and electromagnetic loads. These loads arise from the cabling, coil manufacturing, cooling, and magnet operation. In order to optimize the manufacture and operating conditions, the mechanical behavior of CORC ® cables must be understood for the different relevant loading conditions. The cable configuration with many contact interactions between tapes and the non-linear behavior of the materials during the production and operating conditions makes the modeling challenging. Detailed finite element (FE) modeling is required to account for these complexities. The FE modeling allows an accurate calculation of the stress-strain state of the cable components under various loads and avoids time-consuming large-scale experimental optimization studies. This work presents a detailed FE modeling of the 3D stress-strain state in a CORC ® wire under bending load. The elastic-plastic properties of the individual tape composite materials and its temperature dependence are taken into account. The FE model is experimentally validated by a multi-layer CORC ® bending test performed by Advanced Conductor Technologies LLC. A critical intrinsic tensile strain value of 0.45% is taken as the threshold where the individual tape performance becomes irreversibly degraded. The proposed FE model describes the bending test of the CORC ® wire adequately and thus can be used to study other types of loads. A parametric study is ongoing with dependent variables to pursue a further optimization of CORC ® cables and wires for various applications.

The influence of strip tension on contact stress and cold rolling force with strainhardening has been investigated by using a numerical method. Dependences between roll pressure and strip tension for one rolling case have been studied. A comparison of the results provided by an introduced method to the already known methods allowed measurements of inaccuracy when the arc of contact has been replaced by chord and whenthe yield strength value for each step has been replaced by the average value of yield strength. Approaching to the real shape of the deformation zone and step-by-step calculations of strain-hardening increases magnitudes of average normal stress and rolling force. The highest difference between obtained results in comparison with the introduced method and already known methods reaches the largest value in the case with intensely hardening steels without strip tension. The increase of strip tension shows less difference between methods. The introduced method lets to calculate the rolling force for different metals depending on strip tension with more precision. Obtained results of the numerical analysis of the influence strip tension on the average normal stress and rolling force were summarized in the form of functions convenient for engineering calculations, with inaccuracy less than 5%.

Due to an error in the production process, the caption for figure 2 is incorrect. It should correctly read 'Figure 2. Configuration of SuperPower 2G HTS Tape SCS#030'.

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