The effects of transverse compressive stress on the critical current,
Ic, of two different superconductors, bronze processed Nb
3Sn single-core wires and Nb-tube processed Nb
3Al multifilamentary wires, have been measured. It has been found that both type of wires show basically the same stress dependence of
Ic.
Ic's decrease monotonically with externally applied stress and
Ic-degradations become larger with increasing magnetic field. The process of
Ic-degradations can be divided into 2 stages. In the first stage the
Ic-degradation rate with stress is relatively small and lowered
Ic's due to applied stress completely recover to the unstressed value when stress is removed, while in the second stage the
Ic-degradation rate with stress is large and permanent
Ic-degradations remain after removal of load. In the first stage of
Ic-degradations due to stress, from an analysis based on the elasticity theory of the stress state of superconducting filaments of the multifilamentary wire under transverse compressive stress, it is suggested that the sensitivity of the critical current to transverse stress is substantially the same as that to axial stress. On the other hand, in the second stage it can be speculated that nonuniform deformation of the matrix may cause local bends or kinks in the superconducting filaments and these damages to the filaments may be chiefly responsible for the
Ic-degradations. The stress beyond which the second stage starts are 150MPa and 700MPa for Nb
3Sn and Nb
3Al wires, respectively. This stress seems to correspond to the yield stress of the matrix material of the wires where superconducting filaments are embedded.
抄録全体を表示