Residual Strain in a ${\rm Nb}_{3}{\rm Sn}$ Strand Mounted on a Barrel for Critical Current Measurements

With the aim of clarifying the relationship between lattice deformations and superconducting properties of Nb3Sn technological wires we have carried out high-energy x-ray diffraction experiments at the European Synchrotron Radiation Facility (ESRF) in Grenoble on individual samples of multi-filamentary internal-tin-type Nb3Sn wires. In particular, a test probe developed at the University of Geneva allowed us to perform these experiments at 4.2 K, while applying an axial tensile load to the specimen. In this way, the lattice parameter values of all the constituents (Nb3Sn, Nb, Cu) were determined, in both the parallel and orthogonal directions with respect to the applied load axis, as a function of the applied strain. The experiments were performed on industrial wires, which were reinforced by a stainless steel outer tube, applied before the Nb3Sn reaction heat treatment, in order to evaluate the effect of an additional pre-compression strain. The relation between the microscopically determined crystalline lattice deformations and the measured applied strain is discussed as a basis for the analysis of the superconducting performances of Nb3Sn wires subject to mechanical loads.

Section: Lattice Parameterssupporting

confidence: 84%

Section: Lattice Parameterssupporting

confidence: 84%

Direct observation of Nb₃Sn lattice deformation by high-energy x-ray diffraction in internal-tin wires subject to mechanical loads at 4.2 K

Muzzi

Corato

Corte

et al. 2012

“…The differences between the Nb 3 Sn pre-strain values found in this work and those derived from I c versus strain measurements, for instance, by using Walters springs, may be partly explained by the influence of the sample geometry on the Nb 3 Sn stress state inside the composite. As an example, the axial and transverse Nb 3 Sn lattice parameters measured by neutron diffraction in a PIT B215 wire mounted and reacted on a Ti-V-Al critical current measurement barrel at 10 K are 5.272 Å and 5.283 Å, respectively [28]. The corresponding lattice parameters measured in the straight wire by synchrotron XRD are 5.276 Å and 5.278 Å, respectively.…”

Section: Discussionmentioning

confidence: 95%

“…The corresponding lattice parameters measured in the straight wire by synchrotron XRD are 5.276 Å and 5.278 Å, respectively. Thermal cycling [28] and wire bending [29] can further influence the Nb 3 Sn stress state.…”

Section: Discussionmentioning

confidence: 99%

Stress distribution and lattice distortions in Nb₃Sn multifilament wires under uniaxial tensile loading at 4.2 K

Scheuerlein¹,

Michiel²,

Buta³

et al. 2014

The lattice parameter changes in three types of Nb 3 Sn superconducting wires during uniaxial stress-strain measurements at 4.2 K have been measured by high-energy synchrotron x-ray diffraction. The nearly-stress-free Nb 3 Sn lattice parameter has been determined using extracted filaments, and the elastic strain in the axial and transverse wire directions in the different wire phases has been calculated. The mechanical properties of the PIT and RRP wire are mainly determined by the properties of Nb 3 Sn and unreacted Nb. This is in contrast to the bronze route wire, where the matrix can carry substantial loads. In straight wires the axial Nb 3 Sn pre-strain is strongest in the bronze route wire, its value being smaller in the PIT and RRP wires. A strong reduction of the non-Cu elastic modulus of about 30% is observed during cool-down from ambient temperature to 4.2 K. The Nb 3 Sn Poisson ratio at 4.2 K measured in the untwisted bronze route wire is 0.35. The present study also shows that the process route has a strong influence on the Nb 3 Sn texture.

“…Soldering the superconducting composite onto a sample holder invariably influences the strain state after cool down, and the tensile strain limit at which an irreversible degradation is observed is influenced by the materials properties of the sample holder and the solder [30]. The bending of the wire on springs also influences the wire internal stress state [30,32,33]. Thus, the difference in ε irr−5% of Bi-2212 wires that have been reported could be due to the influence of the test configuration.…”

Section: Discussionmentioning

confidence: 99%

Strain induced irreversible critical current degradation in highly dense Bi-2212 round wire

Bjoerstad¹,

Scheuerlein²,

Rikel³

et al. 2015

The strain induced critical current degradation of overpressure processed straight Bi-2212/Ag wires has been studied at 77 K in self-field. For the first time superconducting properties, lattice distortions, composite wire stress and strain have been measured simultaneously in a high energy synchrotron beamline. A permanent Ic degradation of 5% occurs when the wire strain exceeds 0.60%. At a wire strain of about 0.65% a drastic n-value and Ic reduction occur, and the composite stress and the Bi-2212 lattice parameter reach a plateau, indicating Bi-2212 filament fracturing. The XRD measurements show that Bi-2212 exhibits linear elastic behaviour up to the irreversible strain limit.