Interpretation of Compressive Strain Causing Critical Current Degradation of Bi2212 Round Wires

High-temperaturesuperconducting Bi
₂
Sr
₂
CaCu
₂
O
_x
(Bi2212) round wires (RWs) are multicomponent composite structure withsuperconductor Bi
₂
Sr
₂
CaCu
₂
O
_x
as the fiber core, metallic silver (Ag) as the matrix, and a silver-magnesium alloy sheath (Ag-Mg) wrapped on the outside. The microstructure of Bi2212 RWs is found to be extremely complicated due to complex preparation process, which mainly manifested in irregular Bi2212/Ag interfaces and porous structure of Bi2212 filaments. For such Bi2212 multifilament RWs, many studies reported applied strain causing degradation of the critical current (
${I_c})$
, but only a few focused on exploring the mechanism of strain dependence of the
${I_c}$
degradation during a larger strain range spanning from compressive to tensile one. Based on our previous work of modeling the
${I_c}$
degradation under
applied tensile strain
, in this work, we tried to further interpret why
applied compressive strain
makes the
${I_c}$
of Bi2212 RWs drop rapidly. By using the numerical model on fully taking account of irregular Bi2212/Ag interfaces, we found that buckling deformation of Bi2212 wires, even smaller, arises after heat treatment. And, for a Bi2212 composite RW with thermal residual strain accumulation, under applied compressive strain, the results indicate that the reason of the critical current degradation is essentially tensile failure of Bi2212 filaments, which results from buckling deformation of the whole wire. Furthermore, on the current shunt model we proposed previously, the relation curve of the
${I_c}/{I_{c0}}$
versus applied compressive strain was obtained, which is well-agree with experimental data. And on these results, electromechanical analysis revealed that this relation of
${I_c}/{I_{c0}}$
versus applied compressive strain results both from tensile damage of Bi2212 filaments, and subsequently current flowing cross the Bi2212/Ag interface and into Ag matrix near cracks inside filaments.