Magneto-optical imaging study of the crack formation in superconducting tapes caused by applied strain

摘要

The crack formation in filaments of multi-filamentary Bi_2Sr_2Ca_2Cu_3O_x tapes as function of applied longitudinal strain is visualized by means of magneto-optical imaging. Strain is applied at the desired temperature inside a helium flow cryostat. Cracks form transverse to the current carrying direction of the filaments. Before the tape breaks entirely, all filaments have formed a large number of transverse cracks, spaced with an average crack distance of ≈200 μm. The crack formation is compared with the degradation of the critical current as a function of the applied strain. The critical current degrades already before the first crack is observed. This is explained by the limited number of filaments visible in the experiment.