The influence of thermal precompression on the mechanical behaviour of Ag-sheathed (Bi,Pb)2223 tapes with different matrices

• Published in: Physica. C, Superconductivity Superconductivity, 2002-07, Vol.371 (3), p.173-184
• Main Authors: Passerini, Reynald, Dhallé, Marc, Giannini, Enrico, Witz, Grégoire, Seeber, Bernd, Flükiger, René
• Format: Article
• Language: English
• Subjects: Bi,Pb tapes; Filling factor; Irreversible strain; Mechanical properties; Tensile strain
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/S0921-4534(01)01076-0

The behaviour of the critical current in longitudinally strained Bi,Pb(2223) tapes shows a strain-insensitive plateau up to an irreversible strain limit ε irr. For higher strains, the formation of cracks induces an abrupt decrease of the critical current. We investigate the relationship between precompression and irreversible strain limit with a set of tapes made with different filling factors as well as an in situ Inconel 600-reinforced tape. I c( ε) curves were measured in a longitudinal strain apparatus at 77 K. The precompression at the measurement temperature is numerically estimated for each sample as well as the evolution of precompression during the cool-down. These calculated values are compared to the fracture susceptibility of extracted filaments, which gives an empirical estimate of the precompression. The main hypothesis of the “Irreversible I c Reduction Model” is confirmed, i.e. the irreversible strain limit essentially depends on precompression. However, we also found that the regime where I c remains constant contains a tensile component: the plateau extends beyond the external tensile strain needed to relieve the thermal precompression and includes a regime where the ceramic is further elongated non-destructively. This non-destructive deformation can be understood as a “connected-grains” behaviour, and extends the strain-insensitive plateau ∼0.1% beyond the precompression strain. This value is confirmed with a three points bending experiment performed on single filaments which gives a similar value for the bending failure strain. A comparable regime was found to exist also under compressive strain. These non-destructive regimes are of great importance for practical applications since up to a certain level the precompression can develop without any I c degradation.