Mechanical property and its influence on the critical current of Ag/Bi2223 tapes

Abstract

The stress-elongation (R-A) curve has been experimentally characterized as follows. The initial quasi-elastic region (stage I) was very narrow where the pure Ag component had already yielded due to the thermal contraction. In the following stage II, the slope was reduced owing to the yielding of the Ag alloy. Stage III was defined as the macroscopic multiple fracture taking place in the oxide layer. The R-A behaviour at 77 K has been theoretically simulated based on the rule of mixture. The oxide layer was exerted by a large compressive residual stress due to the thermal contraction. Applying tensile elongation, its compressive stress reduced and became zero at a specific elongation A r1 , after which the sign of stress changed to tensile and its quantity increased. When the tensile stress of the oxide layer reached its fracture strength, macroscopic yielding was expected. Such a result obtained from the simulation can describe well the experimental R-A curve as well as the following elongation dependence of critical current. The critical current decreased linearly with increasing tensile elongation from the beginning of stage I and its gradual decrease followed in stages II and II . This elongation dependence of critical current was reversible in stages I and II, but irreversible in substage II . In stage III corresponding to the plastic deformation region, the critical current was reduced largely due to the macroscopic crack formation.

Mechanism for the uniaxial strain dependence of the critical current in practical REBCO tapes

“…In this case, the retained strain was 0.41 % and 0.48 % for the Superpower and SuNAM tapes respectively. In several publications [10,23], the 95% retained strain (A(Ic/Ic0=0.95)) limit has been reported as the reversible strain limit for both REBCO and BSCCO tapes. In the case of BSCCO tapes, it is possible to use the 95% retained strain (A(Ic/Ic0=0.95)) as the strain limit because it has been verified experimentally [24,25].…”

Residual strain dependence on the matrix structure in RHQ-Nb3Al wires by neutron diffraction measurement

“…• C (T H ) [15,17]. Then, as temperature decreased to room temperature (T R ), the residual strain increased with an increase in the stress between the Nb 3 Al filament and the matrix material owing to the difference in their CTE.…”

Applicability of Weibull Distribution to Description of Distributed Normalized Critical Current of Bent-Damaged Bi2223 Composite Tape

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] Heterogeneous damage occurs, and the damage evolution behavior differs from specimen to specimen and from location to location within a specimen. [9][10][11][12][13][14] Accordingly, when a number of specimens are tested, the critical current differs from specimen to specimen.…”

“…Because the " r is negative (compressive) in the Bi2223 composite tape, as has been demonstrated by X ray diffraction analysis, 7,8) the actual fracture strain of the filaments in the composite tape is by À" r higher than the intrinsic fracture strain " f of the filaments alone. 2,4,[6][7][8]11,14) The " f À " r value is different from location to location within a specimen as well as from specimen to specimen. In the preceding works, 11,12) the heterogeneous damage behavior was formulated by the distributed " f À " r values and was correlated to the distribution of critical current values.…”