Three stage behavior in stress-elongation curve of multifilamentary Bi2223 tapes

摘要

Complicated stresses are exerted in the PIT processed Bi2223 tapes during the winding stage of magnet manufacturing process and large electromagnetic forces are applied during its operation. Therefore the knowledge of mechanical properties is crucial for the practical application. The tapes consisting of multi-oxide-filaments with the metal matrix show a three stage behavior. The first elastic region (stage I) is very narrow and followed by the stage II, where the slope of stress - elongation curve decreased gradually. Then the macroscopic yield and the plastic deformation over the whole tape took place in stage III. When the change of electric voltage was simultaneously monitored, the voltage turned on to increase from the beginning of stage II and its increasing rate accelerated in the stage III. Their change is related to the formation of microcracks and the macroscopic fracture in the oxide layer, respectively. The yield strength is known to be strengthened greatly by using the silver alloy matrix. However, it should be noted that an irreversible degradation in the oxide layer starts from the beginning of stage II prior to the macroscopic yield.