Influence of dynamic and static stresses to mechanical and transport properties of Ag/Bi2223 composite superconductors

Mechanical properties under static stress of Bi2223 monofilamentary tapes are characterized. The narrow true elastic region (stage I) is followed by the stage II, where a gradual decrease of the slope of stress-strain curve was observed, accompanied by voltage increase. This suggests that a number of microcracks are generated over the whole specimen and a few of them grow in macroscopic scale. The macroscopic yielding and the multiple fracture take place in the oxide layer (stage III). During the fatigue test, the V-I curves were measured at zero load and the n-value was determined. For stage II, the critical current decreased greatly after one cycle and decreased gradually over several hundred cycles, then reached to a non-zero constant value depending on the applied maximum stress. Applying the two phase model, the change of stress level induced in each component has been assessed.