Analysis of transport critical current density in a bent BiPbSrCaCuO silver-sheathed tape

The experimental results on the magnetic behavior of the transport critical current density in a bent Bi based superconducting tape have shown that the irreversible strain limit ε_irrev for the onset of permanent strain damage to Ag sheathed superconductors is not dependent on the magnetic field, nor does the normalized I_c(H, ε) I_c(0, ε) current depend on the strain at least up to 0.5 T at 77 K. Such a behavior has been attributed to two reasons: (1) The intrinsic pinning properties are unchanged in a bent tape; (2) The strain effect is extrinsic and arises from superconductor cracks. Thus, based on these arguments a Josephson junction tunneling model with cracks in between the grain boundaries is proposed to explain the J_c behavior quite well for a bent granular high-T_c superconducting tape. Our model calculation shows that the critical current density of high-T_c superconductor may be enhanced by increasing the strain tolerance ε_irrev and the ε_irrev is determined by the properties of Ag sheathed tape and its related material parameters, which are dependent on the connectivity of the grain boundaries.