Influence of Edge Crack Propagation on Critical Current Degradation of REBCO Tape Studied by Phase-Field Fracture Method and Current Shunting Model

For efficiency and cost savings during manufacturing, a fixed wide REBa2Cu3O7-x (REBCO) tape is usually mechanically slit to a width required by varying applications, whereas the multiple edge cracks are induced in this process. In physics, it is widely recognized that the critical current of REBCO tape is degraded with tensile strain, and excessive strain causes crack growth. We are curious about how the edge crack grows under tensile strain, thereby further affecting the critical current performance. Therefore, we first introduced the phase-field method (PFM) to analyze the cracking and fracture behavior. After building a numerical model containing an edge crack and solving it by the finite element method, we presented the propagation path of the edge crack under tension and obtained the quantitative correlation between fracture ratio (crack depth/tape width) and tensile strain. Furthermore, since cracks impede the current flow and make the current shunted to the metal layer, resulting in critical current degradation, we adopted a current shunting model that considers the obstacle of cracks to investigate the relationship between critical current degradation and fracture ratio. Moreover, employing the intermediate variable of fracture ratio, we obtained the I-c - epsilon curve of REBCO tape. By comparing the calculated I-c - epsilon curve with previous experimental data, the critical current degradation with tensile strain was very well interpreted by the propagation of the edge crack induced by mechanical slitting.