Tensile and bending fracture behaviors and their influence on critical current of multifilamentary Bi2223/Ag/Ag-Mg composite tape

The process of damage extension under bending and tensile strains at room temperature and its influence on critical current at 77 K under zero magnetic field were studied for a mutifilamentary Bi223/Ag/Ag-Mg alloy superconducting composite tape. Under the tensile strain, the damages such as transverse cracking of the Bi2223 filaments, longitudinal cracking along the filament axis and interfacial debonding between Bi2223 and Ag took place. Under the bending strain, in addition to these damages, protrusion of the compressive side due to buckling, accompanied by compressive fracture of the filaments, was observed. From the analysis of the residual stress, tensile stress-strain curve and tensile damage-induced reduction in critical current, the Young's modulus, residual strain and intrinsic tensile fracture strain of the Bi2223 filaments at room temperature were estimated to be 98 GPa, -0.16% and 0.09similar to0.13%, respectively. The change of critical current with bending strain was calculated by substituting these estimated values and compressive strength of the filaments as a variable into the proposed model in which the influence of the damages both in tensile and compressive sides on critical current was incorporated. From the comparison of the calculation- and experimental results, the compressive strength of Bi2223 filaments was estimated to be several times higher than the tensile one.