In order to clarify the mechanical properties and their influence on the critical current of DI-BSCCO tapes with and without lamination, mechanical tests and critical current measurements were performed, and the corresponding residual strain exerted on the BSCCO component was measured by a neutron diffraction technique. Also the residual strain analysis was calculated using the rule of mixtures. The measured modulus of elasticity, the second slope, and the stress corresponding to the force free strain were self-consistently explained on the basis of this analytical model. The calculated residual strain in the BSCCO component was found to be nearly identical with that determined by neutron diffraction for all DI-BSCCO tapes except for the case of the low strength insert tape. The difference between the strain corresponding to 95% I c retention and the force free strain was explained by the fracture strain of BSCCO filaments. An approximate expression to evaluate the residual strain in the BSCCO filaments is also presented along with a procedure for estimating the initial temperature T 0 at which the residual strain starts to accumulate during cooling after the fabrication heat treatment.

Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. In order to elucidate the effect of uniaxial strain on the critical current of practical REBCO tapes (REBa2Cu3O7-d, RE = Y and Gd) fabricated by Superpower and SuNAM, two types of critical current measurements were carried out. In the first, the tape sample was attached directly to a universal testing machine and pulled under a tensile load. In the second, the tape was soldered to a Cu-Be springboard (SB) and then attached to the testing machine and then pushed or pulled in order to apply both tensile and compressive strains to the tape sample. An inverse parabolic behavior was observed for the uniaxial strain dependence of the critical current of both tapes.Using synchrotron radiation, the local strain exerted on the REBCO layer was measured at room temperature under the conditions used for the two techniques for making Ic measurements. On the basis of these room temperature data, the local strain exerted on the REBCO layer at 77 K was numerically evaluated.A one-dimensional chain model for current flow in the REBCO material with fractional lengths of A-domains and B-domains oriented along the uniaxial strain direction is proposed. The model can explain the parabolic strain behavior of the critical current and shows that the strain at which the peak in Ic occurs, is not only determined by pre-compression or pre-tension on the superconductor at the operating temperature, but also by the ratio of the fractional amounts of the two domains.

The stress/strain behavior of the surround Cu stabilized YBCO coated conductors and its influence on critical current were precisely investigated. The internal strain exerted on the superconducting YBCO layer was determined at 77 K by using a neutron diffraction technique at JAEA. The initial compressive strain decreased during tensile loading and changed to a tensile component at the force free strain (A ff ), where the internal uniaxial stress becomes zero in the YBCO layer. The A ff was evaluated to be 0.19-0.21% at 77 K. The critical current measurements were carried out under a uniaxial tensile load at 77 K. The strain dependence revealed a characteristic behavior, where a maximum was observed at 0.035%. Thus it was made clear that the strain at the critical current maximum does not correlate with A ff for YBCO coated conductors.

The deformation behaviour of a YBa2Cu3Ox (YBCO)-coated conductor based on Ni–W substrate and its influence on the critical current were precisely investigated. From a room temperature tensile test, the change of permanent strain as a whole of the coated conductor was divided into two regions of micro- and macroscopic yielding. The precise lattice constant measurement by synchrotron radiation at Spring8 revealed that the permanent strain in the YBCO layer was characterized by two regimes related just to the two regions of yielding mentioned above. In the micro-yielding region, the permanent strain in the YBCO layer was identical with that in the metallic components, suggesting that the YBCO layer behaves elastically and any damage-like cracks were not introduced. In the macroscopic yielding region, the smaller permanent strain in the YBCO layer compared with the metallic components suggested that damage-like cracks were introduced in the YBCO layer during loading and remains under zero external load. There the invariant of total length is accommodated by the existence of damage-like cracks. The reversibility of the critical current was evaluated by loading/unloading experiments. The permanent strain ensuring the reversible limit and the corresponding applied strain were found to be 0.17% and 0.52%, respectively. This reversible limit coincided with the limit of micro-yielding. Furthermore the irreversible degradation of the critical current as a function of strain is suggested to relate to the macroscopic yielding.

A reversible effect of strain on the critical current (Ic) has been reported for REBa2Cu3O7−δ (REBCO) coated conductors. In this study, the strain sensitivity of Ic was compared for GdBCO coated conductors with different crystal orientations. Extremely small strain sensitivity was confirmed from tensile and bending tests at 77 K for a GdBCO film with the [110] direction parallel to the tape length (Gd-F), while a GdBCO film with the [100] or [010] direction parallel to the tape length (Gd-I) has much stronger strain dependence of Ic. To compare the strain sensitivity of Ic based on internal strain, the lattice strain was evaluated for a GdBCO film in a composite conductor by employing a diffraction technique using synchrotron radiation. The lattice strain was determined along both the a- and b-axes for the orthogonal domains that are generated by the twin structure of GdBCO film. A distinct difference in the 2D strain state that depended on the crystal orientation was revealed for the GdBCO coated conductors. In Gd-I, the lattice strains along the axial and lateral directions are tensile and compressive under tensile loading, respectively, that is, the 2D internal strain state is anisotropic. On the other hand, an almost isotropic 2D strain state was confirmed in Gd-F. In addition, the strain components along the crystal axes in Gd-F are much smaller than the axial strain components in Gd-I. This difference in the internal strain state is attributed to the difference in strain sensitivity between the GdBCO coated conductors with different crystal orientations. The contributions of the strain components along the a- and b-axes to Ic are discussed on the basis of the measured strain sensitivities and internal strains for two conductors.