Finite Element Investigation Into Axial Strain Tests on a High-Temperature Superconducting Cable

A proposed method of replicating hoop strain experimentally within straight sections of high-temperature superconductor (HTS) cable was investigated through finite element analysis (FEA). In operation, a cable-wound coil will experience very large (up to 1000 kN/m or more) electromagnetic loads as well as hoop strains of over 0.2%, and so extensive mechanical testing of HTS cables is required to understand their operational limits before designing magnets. For electromechanical testing, transverse loads can be created with a just short section of cable inserted into a magnet, but axial hoop strain is more challenging to create due to the necessity of building a 3D coil setup. To reduce the cost and complexity of testing a full magnet, an experimental method to replicate hoop strain conditions was proposed by a group from MIT-PSFC during the testing campaigns of the VIPER HTS cable. In the experiments, the cable was axially strained at room temperature by clamping on the cable in two areas and applying tensile force between the clamps. Additional strain was induced by the cooldown process. In this study, we use finite element analysis to replicate the strain conditions obtained through the room-temperature tensile testing to provide insights into the strengths and limits of that type of experiment. The results obtained with FEA are compared to the experimental data available. Our analysis indicates that 65% to 85% of the axial strain on the jacket's outer surface in the unclamped region transfers to the tapes, with the innermost tape experiencing the highest strain. Experiments of this kind together with FEA could be helpful tools for characterizing superconducting cables used in large magnets without the need for building full-size systems.