Internal residual strain and critical current maximum of a surrounded Cu stabilized YBCO coated conductor

Abstract

The deformation behavior of the surrounded Cu stabilized YBCO coated conductor based on the Hastelloy substrate and its influence on the critical current were precisely investigated. The mechanical properties were assessed at room temperature and 77 K. The greatest contribution was brought by two metallic components of the Hastelloy substrate and Cu stabilized layers. The internal strain exerted on the superconducting YBCO layer was determined directly by using synchrotron radiation facilities. The thermally induced residual strain with compressive component decreased during the tensile loading and changed to a tensile component at the force free strain (Aff), at which the internal stress becomes zero in the YBCO layer. Beyond Aff, the increasing rate of internal strain slowed down, suggesting brittle behavior, that is, the formation of micro-cracks. The applied strain dependence of the critical current could be divided into two regions. In the reversible region, the strain dependence obeyed the intrinsic strain effect and was well expressed by the Ekin formula. Beyond the reversible limit, the critical current decreased rapidly with strain. The degradation is suggested to be attributed to the formation of cracks in the YBCO layer. The force free strain evaluated from the mechanical properties was 0.26%. On the other hand, the strain at the critical current maximum was observed to be 0.035–0.012%. These facts suggest re-examining the hypothesis supposing that the critical current maximum appears at the force free strain in YBCO coated conductors.

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

“…Best fits to the data are found by restricting the fits to the strain near the peak and similar values were found to those in Table 7. At high strains, Eqn (16) describes a linear strain behavior for Ic associated with dissipation predominantly in a single domain and the linear approximations made, for example in Eqn (15). As shown in Figure 9, the Ic data can be accurately described using a second order polynomial out to high strains, consistent with the eventual break-down of the linear approximations.…”

“…Furthermore, an important strain parameter is the force free strain (Aff) at the operating temperature for Ic measurements [15]. The force free strain at 293 K is shown for the Superpower tape and the SuNAM tape in vs Aa is not unity, but shows systematic changes such that the slope for the tapes mounted on the SB are higher than that for the free standing tapes.…”

“…Rewriting Eqn (13) - (15) for the B-domains, we simplify the algebra by taking (0) and (0) to be the same in both domains. Hence the condition for a crossover in Tc and Jc between the two domains occurs when , (0 (11), we can calculate the value of Jc at the standard E-field criterion,…”

Tape Length-Dependence of Critical Current and <i>n</i>-Value in Coated Conductor with a Local Crack

“…13) In fabrication and service, they are subjected to thermal, mechanical and electromagnetic stresses. When the superconducting layer is cracked by such stresses, the critical current I c is reduced (YBCO, 4,5) DyBCO, 69) SmBCO, 10,11) GdBCO 12) ). The same situation occurs also in the filamentary Bi 2 Sr 2 Ca 2 Cu 3 O 10+x (Bi2223), 1315) Nb 3 Sn, 16) Nb 3 Al 17) and MgB 2 18,19) conductors due to the formation of collective cracks (cracks composed of successively cracked filaments in a transverse cross-section 15,16) ).…”

Effects of Heterogeneous Cracking of Superconducting Layer on Voltage-Current Curve, Critical Current, and <i>n</i>-Value in High-Temperature Superconducting Layer-Coated Conductor Tape

“…(2) and (3) to the measured V-I curves of the cracked DyBCO-coated conductor with a length L 0 = 1.5 cm. 8) The I c and n-value of the non-cracked section with a length L 0 = 1.5 cm were I c0 = 200 A and n 0 = 40, respectively, as in our recent work.…”