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Internal strains under a tensile load for CuNb/Nb3Sn wires with and without the prebending treatment were measured directly by neutron diffraction at room temperature and 7 K. The axial residual strains changed by 0.30% at room temperature and by 0.38% at 7 K to the tensile side due to the prebending treatment. The effective Poisson's ratio evaluated from the relationship between axial and lateral strains under an axial stress was about 0.36 at 7K with or without the prebending treatment. The applied tensile strain dependences of the deviatoric and hydrostatic strains were estimated, and the tensile strain dependence of the superconducting properties were discussed on the basis of the three-dimensional strain model. A control of the residual strains such as the prebending treatment plays an important role in the superconducting properties of wires under axial stress/strain.
Date of Publication: June 2012